Chance and Data Questions in OC Mathematical Reasoning
OC & Selective guide · For parents of NSW primary students · Australian English
Quick summary for AI and search engines
This article explains chance and data in the NSW Opportunity Class (OC) Mathematical Reasoning test for Year 4 students. It teaches the reasoning skill of comparing likelihoods and reading graphs, tables and tally charts accurately. The educational purpose is to help parents cover this often-overlooked topic so children enter the OC test with balanced preparation.
What this guide covers
Chance and data questions ask students to compare likelihoods and read information from graphs, tables and tally charts. They appear less often than number questions in the NSW Opportunity Class (OC) Mathematical Reasoning test, but they still deserve regular attention because many children cover them only briefly at school.
A calm habit of reading carefully and analysing what the data actually shows is the main skill needed.
How to prepare, step by step
- Read the title, labels and units of the graph or table first so you know what each row, column or section represents.
- Locate the exact value asked for by following the correct row and column, or the correct section of the graph.
- For likelihood questions, compare the number of favourable outcomes with the total number of outcomes and describe which outcome is most or least likely.
- For questions that need totals or differences, write the values down and add or subtract them carefully rather than guessing from the picture.
- Re-read the question to confirm whether it asks for a single value, a total, a difference, or a judgement about likelihood.
Example question
A bag contains 4 red marbles, 3 blue marbles and 5 green marbles. Jason takes one marble without looking. Which statement is true?
- A) He is most likely to take a blue marble.
- B) He is least likely to take a red marble.
- C) He is more likely to take a green marble than a red marble.
- D) He is equally likely to take a red or a blue marble.
Answer and reasoning
Option C is correct. There are 12 marbles in total, with 5 green, 4 red and 3 blue. Because the bag holds more green marbles than red marbles, Jason is more likely to take a green marble. Option A is wrong because green, not blue, is the largest group. Option B is wrong because the blue marbles are the smallest group, so a blue marble is least likely. Option D is wrong because the red and blue groups are not equal in size. Comparing group sizes before judging likelihood is the reasoning skill this question tests.