The probability scale
The Maths Habit
Ola says it will either snow tomorrow or it will not,
so snow is an even chance.
Is Ola right?
No: two outcomes are not always equally likely
- Impossible
- It cannot happen. Probability 0.
- Even chance
- Just as likely to happen as not. Probability ½.
- Certain
- It must happen. Probability 1.
How likely is this?
You pick a red sock from a drawer of only black and grey socks.
ImpossibleA letter is picked at random from the word MATHS. It is A.
UnlikelyA month is picked at random. It has 31 days.
LikelyA whole number from 1 to 10 is picked at random. It is odd.
Even chance
You roll a number bigger than 1 on an ordinary dice. How likely is this?
You pick a white counter from a bag of 5 white and 5 black counters. How likely is this?
You roll a number bigger than 1 on an ordinary dice. How likely is this?
You pick a blue counter from a bag of 1 blue and 7 red. How likely is this?
You roll a number bigger than 1 on an ordinary dice. How likely is this?
A spinner is numbered 1 to 8. It lands on 9. How likely is this?
You roll a number bigger than 1 on an ordinary dice. How likely is this?
A card is picked from 3 yellow cards and 3 green cards. It is green. How likely is this?
You roll a number bigger than 1 on an ordinary dice. How likely is this?
A whole number from 1 to 10 is picked. It is less than 11. How likely is this?
Answer sheet
Put these in order, least likely first: rolling a 6, a coin landing on heads, picking a red from 9 red and 1 blue.
6, heads, redA bag holds 3 red and 3 blue counters. One blue is taken out. Is picking a red now likely, unlikely or an even chance?
Likely
A spinner has 10 equal sections. 7 are blue. It is spun once. How likely is it to land on blue?
LikelyA fair dice is rolled.
Even chance, at ½
Mark the probability of an even number.4 red counters and 1 blue. Kai says blue is an even chance, as there are two colours. Is Kai right?
No: unlikely, 1 in 5