Selective thinking skills: weaken an argument (8 questions)

Quick Answer

An option weakens an argument when, if it were true, the conclusion becomes less likely even though the stated reason is still true. Most weakeners offer another cause, counter-evidence about the sample or comparison, or a gap between the reason and the conclusion. This page from Braintree Coaching Australia has eight original arguments for Year 5–6 children preparing for NSW Selective thinking skills, one test to apply to every option, and a reason for every wrong answer. It is free and needs no sign-up.

Who is this weaken-the-argument practice for?

This set suits a Year 5 or Year 6 child who can pick out the reason and the conclusion of a short argument and now needs to judge which new fact would damage it. It is skill practice. We do not claim these items match questions on the real test, and we do not know how many argument questions, if any, a sitting contains.

The NSW Department of Education describes the Selective High School Placement Test as computer-based, with Reading, Mathematical Reasoning, Thinking Skills and Writing sections. Thinking Skills is listed at 40 minutes. The department's own Selective practice tests are the place to see the real format. Our Thinking Skills test guide and guide to the new format explain how the section works.

What does it mean to weaken an argument?

An argument gives a reason and draws a conclusion. To weaken it, accept that the reason is true and show that the conclusion is now less likely. Three common ways:

• Another cause. Something else could explain the result.
• Counter-evidence. The sample or the comparison is not what it seemed, or direct evidence points the other way.
• A broken link. The reason is true but does not lead to the conclusion.

Weakening is different from the necessary assumption set, which asks what an argument needs. Here you are given new facts and must decide what each does to the conclusion.

How do we test each option? A worked model

Argument: "Jess's family started watering their lawn with a sprinkler every morning. The lawn is greener than it was last month. So the sprinkler made the lawn greener."

The one test, for every option: If this is true, do I believe the conclusion less?

1. Option: "It rained heavily on most days this month." If true, the rain could have greened the lawn. Do I believe the sprinkler did it? Less. This weakens. It is another cause.
2. Option: "The lawn still has a few brown patches." If true, is the conclusion less likely? No. The lawn can be greener than last month and still have patches. This does not weaken. It is true and on topic, but the conclusion survives. We call it an insufficient objection.
3. Option: "A neighbour's lawn with no sprinkler stayed brown." If true, do I believe the conclusion less? No, more. This strengthens.
4. Option: "The sprinkler is blue." Nothing changes. Irrelevant.

Four answers, one question each time. Only the first made the conclusion less likely.

The questions

For each argument, choose the one option that weakens it. Ask the test question about every option, and say your answer aloud before you look at the explanations.

Question 1. "Hana's class started a ten-minute reading time after lunch. Their average on the term spelling test rose from 14 to 17 out of 20. So the reading time improved their spelling."

• A. At the same time, the class began taking home a weekly list of spelling words to practise.
• B. A class of the same year with no reading time showed no change on the same test.
• C. Hana's class average on the test is still below the average of the other Year 5 classes.
• D. The reading time starts at 1:15 pm.

Question 2. "The Lakeview bakery sold twice as many pies in July as in June. So its new pie recipe has made its pies more popular."

• A. The bakery's pies are baked at 5 am each day.
• B. In a short survey, many July customers said they chose the pies because of the taste of the new recipe.
• C. In July the bakery opened a second shop next to the footy oval, and the finals crowds bought most of the extra pies.
• D. The new recipe costs more to make than the old one.

Question 3. "After the council planted trees along Elm Road, the average summer afternoon temperature on Elm Road was two degrees lower than the summer before. So the trees cooled the road."

• A. Elm Road is still warmer in the afternoons than the park nearby.
• B. Streets all over the city were about two degrees cooler than the summer before, including streets with no new trees.
• C. Nearby streets with no new trees showed no fall in temperature.
• D. Volunteers planted the trees on a Saturday morning.

Question 4. "Every student who joined the chess club last year improved their maths mark. So learning chess improves maths marks."

• A. The chess club meets on Thursdays after school.
• B. Some members improved their maths mark by only a few marks.
• C. Students with the same earlier marks who did not join the club showed no improvement.
• D. Only students who were already working extra hard at maths were allowed to join the club.

Question 5. "Lifeguards at Pool A made four rescues this summer. Lifeguards at Pool B made one. So Pool A is more dangerous than Pool B."

• A. Pool A had about ten times as many swimmers as Pool B.
• B. Pool B is closer to the train station.
• C. Most of Pool A's rescues were in the first week of summer.
• D. Both pools had about the same number of swimmers over the summer.

Question 6. "In Mr Okafor's class, the paper planes with the longest wings flew furthest. So longer wings make a paper plane fly further."

• A. The planes were folded from A4 sheets.
• B. The planes were flown indoors in the school hall.
• C. When the same plane was flown again with its wings trimmed shorter, it flew further each time.
• D. When the same plane had its wings lengthened with tape, it flew further each time.

Question 7. "The school canteen sold about 200 sandwiches each day last week. The school has 400 students. So about half of the students buy a sandwich each day."

• A. The canteen sold a few more sandwiches on Friday than on Monday.
• B. Many students who buy a sandwich buy two on the same day.
• C. The canteen opens at 8:30 am.
• D. No student buys more than one sandwich a day.

Question 8. "The 7:42 train reaches Parkview in 28 minutes. Nina leaves home at 7:30 to catch it. So she will be at Parkview by 8:15."

• A. The 7:42 train is sometimes one or two minutes late.
• B. Parkview station has a new café.
• C. Nina's walk from home to the station takes about two minutes.
• D. Nina's walk from home to the station takes 20 minutes.

Answers and worked explanations

Each question has one option that weakens, one that strengthens, one that is irrelevant and one insufficient objection. The type of weakener is in brackets.

Question 1: A (another cause). Test: if the weekly word list began at the same time, the rise could be from the extra spelling practice, so we believe the reading time did less. B strengthens: a class without reading time did not improve. C is true and on topic, but a class can sit below the others and still have improved, so the conclusion survives. D is irrelevant, because the start time does not touch spelling.

Question 2: C (another cause). Test: if a new shop and a finals crowd made up most of the extra sales, the doubling may have little to do with the recipe, so we believe the conclusion less. A is irrelevant to popularity. B strengthens, because customers named the recipe. D is an insufficient objection: a recipe can cost more and still be more popular.

Question 3: B (another cause). Test: if every street cooled by about the same amount, including those without new trees, something citywide explains the fall, and we believe the trees did less. A is true and on topic, but the park can be cooler and the trees still have cooled the road. C strengthens. D is irrelevant.

Question 4: D (counter-evidence about the sample). Test: if only students already working extra hard could join, they may well have improved anyway, so the club may not be what raised their marks. A is irrelevant. B is an insufficient objection: the claim was that every member improved, and a small improvement is still an improvement. C strengthens, because similar students outside the club did not improve.

Question 5: A (counter-evidence about the comparison). Test: four rescues among ten times as many swimmers is a lower rate than one among fewer, so Pool A is no longer clearly more dangerous. B is irrelevant. C is an insufficient objection: when the rescues happened does not change that there were more of them. D strengthens, because with equal numbers of swimmers the counts are a fair comparison.

Question 6: C (direct counter-evidence). Test: if the same plane flew further with its wings cut shorter, then longer wings are not what made it fly further, and we believe the conclusion much less. A is irrelevant. B is an insufficient objection: the conclusion is about wings, and a plane flown indoors can still show what wings do. D strengthens, because lengthening the wings gave the same result.

Question 7: B (broken link). Test: the reason is true, but 200 sandwiches only means 200 students if each student buys one. If many buy two, fewer than 200 students buy a sandwich, and "about half" is less likely. A is an insufficient objection: a few more on Friday still leaves about 200 a day. C is irrelevant. D strengthens, because it closes the gap and makes 200 sandwiches mean 200 students.

Question 8: D (broken link). Test: the reason (a 28-minute trip) and the departure time are both true, but the argument needs Nina to be on the 7:42 train. A 20-minute walk puts her at the station at 7:50, so she misses it and the conclusion is much less likely. A is an insufficient objection: even two minutes late, the train arrives at 8:12, still before 8:15. B is irrelevant. C strengthens.

What mistake patterns should we look for?

Tally which kind of option your child chose. Each needs a different fix.

Pattern	Seen in	What to practise next
Chose the insufficient objection: true, on topic, conclusion survives	Questions 1C, 2D, 3A, 4B, 5C, 6B, 7A, 8A	Ask "do I believe the conclusion less?" and write yes or no beside the option
Chose an option that strengthens the argument	Questions 1B, 2B, 3C, 4C, 5D, 6D, 7D, 8C	Decide first whether the option helps or hurts the conclusion, then whether it matters
Chose an irrelevant detail about the same scene	Questions 1D, 2A, 3D, 4A, 5B, 6A, 7C, 8B	Underline the reason and the conclusion, and check the option touches one of them
Attacked the reason instead of leaving it true	Any	Remember the reason stays true; only the conclusion becomes less likely

Can my child weaken a new argument without options?

Read this argument and write down one fact that, if true, would weaken it. There are no options this time.

"Since Brookvale Primary held a walk-to-school week, the number of cars in the drop-off zone each morning has fallen by a fifth. So walk-to-school week persuaded families to leave the car at home."

Self-check: a good answer gives another cause or a broken link, for example "road works closed half the drop-off zone that week" or "many families were on holiday that week". Then apply the one test: if your fact is true, do you believe the conclusion less? An answer such as "some families still drove" is true and on topic but does not weaken it, because a fifth fewer cars is still a fall. That is an insufficient objection.

What should we do after this set?

• If most errors were insufficient objections, redo Questions 3, 5 and 7 tomorrow and say aloud why the conclusion survives each one.
• For the assumption version of this skill, open the necessary assumptions set.
• For mixed Selective practice, open the NSW Selective practice tests and resources guide or the Selective sample questions.
• The free mock tests need a free classroom account. Use one when your child is ready for a timed sitting.
• If you want a structured set of full Selective tests after that, see what the Selective course includes and check it matches your child's entry year before buying.

Sources and review

Official source (checked 2026-10-15): NSW Department of Education, Selective High School practice tests: computer-based test with Reading, Mathematical Reasoning, Thinking Skills and Writing; Thinking Skills is listed at 40 minutes. The page names no Thinking Skills question types, so this page does not say argument questions are tested.

Where the questions came from: all eight arguments, the worked model and the transfer task are original Braintree Coaching Australia material written for this page. The names, schools and places are made up. None is taken from an official or third-party paper.

Author: James Rush, content writer, Braintree Coaching Australia.

Answer check: on 2026-10-15 every answer was recomputed and every wrong option checked by a second pass that had the key in front of it, so it tests the arithmetic and the wording, not a cold solve. A blind solve by someone who has not seen the keys and a named teacher review have not yet been recorded for this set. If you find an error, please tell us.

Last updated: 2026-10-15.