Statistics and Probability: Collecting, Displaying, and Interpreting Data
What you must understand
Grade 3 statistics focuses on posing a question, collecting data with tally marks, and displaying results in pictographs, bar graphs, and simple tables. You must read a graph accurately, including its title, labels, and scale, and answer questions about which category is most or least frequent, how many more one category has than another, and the total. Probability at this level is informal: describing events as certain, possible, or impossible, and comparing the likelihood of simple outcomes such as drawing a red or blue counter from a bag.
Traps to watch for
- Ignoring the key: in a pictograph where one symbol stands for 5 votes, half a symbol means 2 or 2.5 depending on the stated key; read the key before counting.
- Scale misreads: on a bar graph counting by 2s, a bar ending halfway between 6 and 8 is 7, not 6.
- Most versus more: "which is most?" asks for the largest category; "how many more?" asks for a difference.
- Missing totals: total responses means adding every category, including the smallest.
- Probability wording: "impossible" means zero chance, not just unlikely; "certain" means it must happen.
Worked example
A tally chart shows 4 students chose soccer, 6 chose hockey, and 2 chose swimming. Total = 4 + 6 + 2 = 12 students. Hockey is most popular. Hockey has 6 − 4 = 2 more votes than soccer. Drawing a student who chose swimming is possible but least likely, because 2 is the smallest group.
Rule of thumb
Before answering any graph question, read the title, both axis labels, and the key or scale. Then compute differences by subtracting and totals by adding.