How to see it
Probability measures how likely something is, from 0, impossible, to 1, certain. To find it, count the outcomes you want and divide by all the possible outcomes. Provided they are equally likely. Write it as a fraction, decimal or percentage. "Not" something is one take away the chance of it.
A worked example
Blue: 5 out of 10, a half. Not red: 7 out of 10. Experiments: toss a coin 50 times, 28 heads. The experimental probability of heads is 28 over 50, 0.56.
The common mistake: counting colours instead of counters
The trap is counting the colours: three colours, so one third. The bag has ten counters, not three colours. Count objects, not types.
Try one
A spinner has 8 equal sections and 3 are shaded. What is the chance it does NOT land on shaded?
- A3/8
- B5/3
- C5/8
- D1/2
Show the answerHide the answer
Right: C, 5/8