The probability scale

Mathematics · Probability · ages 11-13

Name ______________________ Date ____________

A probability of 1 means an event is...
- Impossible
- Certain
- Unlikely
Which of these gives equally likely outcomes?
- Spinning a spinner with 3 red sections and 1 blue section
- Rolling a die with two sixes and no five
- Tossing a fair coin
- Drawing from a bag with 5 red cubes and 1 blue cube
A fair coin is tossed. What is the probability of heads? Give your answer as a decimal.
Answer: ______________
Which number is used for something that is impossible?
- 0
- 1
- 1/2
Which event sits at 0.5 on the probability scale?
- Rolling a 6 on a fair six-sided die
- Drawing the blue marble from a bag with 3 red and 1 blue marble
- Rolling a number greater than 4 on a fair die
- Rolling an even number on a fair six-sided die
Meg has a spinner. Red covers half of it, and blue and green each cover a quarter. Is this spinner fair?
- Yes, all three colors are equally likely
- No, red is more likely than blue or green
- No, blue is more likely than red
A fair six-sided die is rolled 600 times. About how many times would you expect to score a 2?
Answer: ______________
A fair die has 6 faces, and each face is equally likely to land up. Write the probability of rolling any one number as a fraction 1/?. What number goes on the bottom?
Answer: ______________
Which event has a probability closest to 1?
- Rolling a 6 on a fair die
- Picking a red ball from a bag of 9 red balls and 1 blue ball
- Flipping a coin and getting tails
A forecaster gives rain a probability of 0.2 on the 0-to-1 scale. What is the probability it does not rain? Give a decimal.
Answer: ______________

Answer key

For grown-ups. Fold this page away before handing over the rest.

The probability scale W1-mt_vmQJAtAFuy-s1

Certain · 1 is the top of the scale. It means the event will definitely happen.
Tossing a fair coin · A fair coin has two symmetric outcomes, so heads and tails are equally likely.
0.5 · Two equally likely outcomes and one is heads, so the probability is 1/2 = 0.5.
0 · Impossible events sit at the very start of the scale, at 0.
Rolling an even number on a fair six-sided die · Even numbers are 2, 4, 6: three out of six outcomes, which is 1/2 = 0.5.
No, red is more likely than blue or green · Red covers more space than blue or green, so it is not equally likely. The spinner is biased.
100 · Each face has probability 1/6, and 600 divided by 6 is 100.
6 · Six faces, each with an equal chance, means the probability of any one number is 1 out of 6.
Picking a red ball from a bag of 9 red balls and 1 blue ball · 9 out of 10 balls are red, so picking red is very likely, close to the certain end of the scale.
0.8 · Rain or no rain covers everything, so 1 - 0.2 = 0.8.