Ratio Toolkit (Edexcel IGCSE Maths A)

False.

The order that the numbers are in does matter.

The order should correspond with the order in which they are listed in words.

E.g. A ratio of 3 parts white paint to every 2 parts red paint, should be expressed as, W : R = 3 : 2

A ratio written as W : R = 2 : 3 would indicated 2 parts white paint to every 3 parts red paint.

An equivalent ratio is a ratio that represents the same relationship between quantities but with different numbers.

For example, and are equivalent ratios.

To simplify a ratio, divide both sides of the ratio by the same number.

This will find an equivalent ratio with smaller values.

E.g.

To share an amount into a ratio:

1. Find the total number of parts, e.g. 2 + 5 = 7 parts

2. Divide the amount by the total number of parts to find the value of one part, e.g. 84 ÷ 7 = 12

3. Multiply the value of one part by each ratio number to find the share for each part of the ratio, e.g. 2 × 12 : 5 × 12 = 24 : 60

If you are given one part of a ratio rather than the total amount to be shared:

1. Find the value of one part by dividing the given part by its ratio number,
   e.g. 60 ÷ 4 = 15

2. Multiply the value of one part by the other ratio number(s) to find the other part(s),
   e.g. 15 × 3 = 45

True.

A must receive 35 chocolates and B receive 49 chocolates.

When given the difference between two parts:

1. Divide the difference given by the difference in the number of parts to find the value of one part, e.g. 14 ÷ (7 - 5) = 7

2. Multiply the value of one part by the number of parts for each quantity in the ratio to find the amount for each quantity, e.g. 5 × 7 : 7 × 7 = 35 : 49

If two quantities are said to be in direct proportion to one another, then as one quantity increases, the other increases by the same scale factor.

E.g. Doubling one quantity will double the other.

If two quantities are inversely proportional, then as one increases the other decreases.

Both quantities change by the same scale factor.

True.

If two quantities are inversely proportional, multiplying one quantity by a scale factor will divide the other quantity by the same scale factor.

E.g. If 200 builders can build a stadium in 12 months, then doubling the number of builders to 400 will halve the time it takes to 6 months.

False.

If your answer needs to be a whole number when working with proportions, you should round your answer to a whole number.

However, this may not always be the nearest whole number.

For example if you find you need 2.3 bags of flour for a recipe, you should round that up to 3 bags to make sure you have enough.