Define direct proportion .

Two quantities are in direct proportion when increasing or decreasing one by a certain factor changes the other by the same factor . The ratio of the two quantities therefore stays constant.

Define inverse proportion .

Two quantities are in inverse proportion when increasing one by a certain factor decreases the other by that same factor. It works the other way round too: decreasing one increases the other.

True or False? The unitary method can be used for inverse proportion as well as for direct proportion.

True. You still find the value for one unit first, but you use the opposite operation at each step. Where direct proportion divides to reach one unit, inverse proportion multiplies.

True or False? If more robots means less time to build a car, the two quantities are in direct proportion.

False. More robots and less time move in opposite directions, which makes this inverse proportion. Direct proportion would be something like more boxes of cereal giving more cornflakes.

GCSEMathsEdexcelFoundationFlashcardsRatio, Proportion & Rates of ChangeDirect & Inverse Proportion

Direct & Inverse Proportion (Edexcel GCSE Maths: Foundation): Flashcards

Exam code: 1MA1

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FrontDirect & Inverse Proportion
Define direct proportion.

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Cards in this collection (8)

Define direct proportion.
Two quantities are in direct proportion when increasing or decreasing one by a certain factor changes the other by the same factor.
The ratio of the two quantities therefore stays constant.
$2$ boxes of cereal contain $800$ g. Complete the working for $6$ boxes:
the factor is $6 \div 2 =______$ , so the mass is $800 \times______= 2400$ g
The completed working is:
the factor is $6 \div 2 = 3$ , so the mass is $800 \times 3 = 2400$ g
The same factor of $3$ applies to both quantities, which is exactly what makes this direct proportion.
$8$ boxes weigh $60$ kg. Use the unitary method to find the weight of $7$ boxes.
$52.5$ kg.
Divide to find the weight of one box, $60 \div 8 = 7.5$ kg, then multiply by $7$ to get $52.5$ kg.
Define inverse proportion.
Two quantities are in inverse proportion when increasing one by a certain factor decreases the other by that same factor.
It works the other way round too: decreasing one increases the other.
$3$ pumps fill a pool in $12$ hours. How long would $9$ pumps take?
$4$ hours.
The number of pumps is multiplied by $9 \div 3 = 3$ , so the time is divided by $3$ , giving $12 \div 3 = 4$ .
$5$ workers take $20$ hours to finish a job. How long would $8$ workers take?
$12.5$ hours.
One worker would take $5 \times 20 = 100$ hours, because fewer workers means more time, and then $100 \div 8 = 12.5$ hours for eight of them.
True or False?
The unitary method can be used for inverse proportion as well as for direct proportion.
True.
You still find the value for one unit first, but you use the opposite operation at each step.
Where direct proportion divides to reach one unit, inverse proportion multiplies.
True or False?
If more robots means less time to build a car, the two quantities are in direct proportion.
False.
More robots and less time move in opposite directions, which makes this inverse proportion.
Direct proportion would be something like more boxes of cereal giving more cornflakes.

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