Fraction and percentage - WJEC

Fractions and percentages represent part of a whole number. They can be used to increase or decrease a value by a given proportion.

Fraction and percentage

\frac {2} {7} or 'two sevenths' means two parts out of seven.

To find \frac {2} {7} of a value, you must first divide by 7 to find what \frac {1} {7} is worth, and then multiply by 2.

To find a fraction of an amount:

  1. Divide by the denominator
  2. Multiply by the numerator
QQuestion

Calculate \frac {2} {7} of 84.

A

24.

  1. Divide by the denominator: 84 ÷ 7 = 12
  2. Multiply by the numerator: 12 x 2 = 24
QQuestion

There are 30 pupils in a class. \frac {1} {5} of pupils play a musical instrument. How many do not play an instrument?

A

\frac {1} {5} of 30 = 30 ÷ 5 = 6 pupils play a musical instrument.

This leaves 30 – 6 = 24 pupils who do not play an instrument.

Finding the original quantity

2/5 of the people on a bus are children. If there are 4 children on the bus, how many people are there in total?

\frac {2} {5} of the value = 4

Divide by 2 to find \frac {1} {5}

\frac {1} {5} of the value = 2

Multiply by 5 to find \frac {5} {5} or 1 whole

10 people in total.

QQuestion

I eat \frac {3} {8} of a chocolate bar and am left with 20 squares, how many squares were there to begin with?

A

\frac {3} {8} has been eaten, which leaves \frac {5} {8}

\frac {5} {8} = 20 squares (now divide by 5)

\frac {1} {8} = 4 squares (now multiply by 8)

1 whole = 32 squares.

QQuestion

Louis’ father increases his pocket money by \frac {1} {3}. He now receives £26 a month. How much was he receiving originally?

A

£19.50

\text {1 whole} + \frac {1} {3} = \frac {3} {3} + \frac {1} {3} = \frac {4} {3}

\frac {4} {3} = £26 (now divide by 4)

\frac {1} {3} = £6.50 (now multiply by 3)

1 whole = £19.50

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