Probability of a single event

The Maths Habit

You win if you take a red counter without looking. Which bag would you pick?

RRRBBBBBBBBBBag A
RRBBag B

Bag B. Most of bag B is red.

What fraction of the counters are shaded?

143527

Probability
How likely something is to happen. It is a number from 0 to 1.
01impossiblecertain
At random
Without looking, so each one has the same chance.
?
Fair
Each side or section has the same chance.
P(red)
The probability of getting red.
R

RRBBB
1all2ones you want3
P(red) =ones you wantall
  1. 1Count them all.This number goes on the bottom.
  2. 2Count the ones you want.Ring them in the bag. This number goes on the top.
  3. 3Write the fraction.Put the top over the bottom.

One counter is taken at random. Find P(red).

RRBBBBB
1Count them all.
7
2Count the ones you want.
2
3Write the fraction.
P(red) =27redall

One counter is taken at random. Find P(green).

GGGGYYYYY
1Count them all.
9
2Count the ones you want.
4
3Write the fraction.
P(green) =49greenall

One counter is taken at random. Find P(red).

RRBBBBB
1Count them all.
7
2Count the ones you want.
2
3Write the fraction.
P(red) =27redall
1Count them all.2Count the ones you want.3Write the fraction.

One counter is taken at random. Find P(blue).

BRRRR
1Count them all.
5
2Count the ones you want.
1
3Write the fraction.
P(blue) =15blueall

One counter is taken at random. Find P(red).

RRBBBBB
1Count them all.
7
2Count the ones you want.
2
3Write the fraction.
P(red) =27redall
1Count them all.2Count the ones you want.3Write the fraction.

One counter is taken at random. Find P(yellow).

YYYYYGGG
1Count them all.
8
2Count the ones you want.
5
3Write the fraction.
P(yellow) =58yellowall

One counter is taken at random. Find P(red).

RRBBBBB
1Count them all.
7
2Count the ones you want.
2
3Write the fraction.
P(red) =27redall
1Count them all.2Count the ones you want.3Write the fraction.

One counter is taken at random. Find P(blue).

BBBBBBBRR
1Count them all.
9
2Count the ones you want.
7
3Write the fraction.
P(blue) =79blueall

1Count them all.2Count the ones you want.3Write the fraction.

1Find P(red).

RBBB
1Count them all.
4
2Count the ones you want.
1
3Write the fraction.
P(red) =14redall

2Find P(green).

GGGGGRR
1Count them all.
7
2Count the ones you want.
5
3Write the fraction.
P(green) =57greenall

3Find P(yellow).

YYYBBBBBBB
1Count them all.
10
2Count the ones you want.
3
3Write the fraction.
P(yellow) =310yellowall

One counter is taken at random. Find P(red).

RRRBGGGG
1Count them all.
8
2Count the ones you want.
3
3Write the fraction.
P(red) =38redall

One counter is taken at random. Find P(yellow).

BBYYYYYRR
1Count them all.
9
2Count the ones you want.
5
3Write the fraction.
P(yellow) =59yellowall

One counter is taken at random. Find P(red).

RRRBGGGG
1Count them all.
8
2Count the ones you want.
3
3Write the fraction.
P(red) =38redall
1Count them all.2Count the ones you want.3Write the fraction.

One counter is taken at random. Find P(green).

GRRBBBB
1Count them all.
7
2Count the ones you want.
1
3Write the fraction.
P(green) =17greenall

One counter is taken at random. Find P(red).

RRRBGGGG
1Count them all.
8
2Count the ones you want.
3
3Write the fraction.
P(red) =38redall
1Count them all.2Count the ones you want.3Write the fraction.

One counter is taken at random. Find P(blue).

YYBBBRR
1Count them all.
7
2Count the ones you want.
3
3Write the fraction.
P(blue) =37blueall

One counter is taken at random. Find P(red).

RRRBGGGG
1Count them all.
8
2Count the ones you want.
3
3Write the fraction.
P(red) =38redall
1Count them all.2Count the ones you want.3Write the fraction.

A bag has 2 mints, 4 toffees and 3 jellies. Find P(toffee).

MMTTTTJJJ
1Count them all.
9
2Count the ones you want.
4
3Write the fraction.
P(toffee) =49toffeeall

Probability of a single event worksheet, page 1

Probability of a single event worksheet, page 2

Answer sheet

Is it right?
Thumbs up: right. Thumbs down: wrong.

  1. 2 red and 6 blue. P(red) = 28

    Right

  2. 2 red and 6 blue. P(red) = 26

    Wrong: the bottom is all 8

  3. 3 red and 4 blue. P(blue) = 37

    Wrong: there are 4 blue

  4. 1 red, 2 blue and 2 green. P(green) = 25

    Right

  5. 4 red and 1 blue. P(red) = 15

    Wrong: there are 4 red

  1. A bag has 2 red and 6 blue counters. Simplify P(red).

    14

  2. A fair dice is rolled. Find P(even number).

    36 = 12

  3. A bag has 4 green and some yellow counters. P(green) = 410. How many are yellow?

    6

  1. Find P(blue).

    35
    RRBBB1Count them all.52Count the ones you want.3Write the fraction.P(blue) =blueall

  2. Find P(red).

    29
    YYYYRRBBB1Count them all.2Count the ones you want.3Write the fraction.P(red) =redall

  3. A bag has 3 green and 8 yellow counters. Find P(green).

    311
Exit tickets to print