Question #92027

2 Answers
May 11, 2017

A = n B
A and B are proportional
A = n/B
A and B are inversely proportional.


It should be clear now.

May 11, 2017

Direct: as one quantity increases, the other also increases.

Inverse: as one quantity increases, the other decreases.


In a proportion, we are comparing the amounts of two quantities.

In a direct proportion, as one of the quantities INCREASES the other also INCREASES.

In an inverse proportion, as one quantity INCREASES the other DECREASES.

MORE boxes of cereal will cost MORE money.
MORE people will eat MORE food.
LESS money will buy FEWER sweets.
MORE clothes will need MORE suitcases.

A task shared by MORE people will take LESS time.
Travelling at a FAST speed will take LESS time for a journey.
If MORE people share a pizza. each person will get LESS.
MORE expensive price means FEWER items can be bought for the same amount of money.

Each type of proportion has a constant. (#k#)

In DIRECT proportion, find the constant by DIVIDING the matching quantities. (they are equivalent fractions:)

#18/27 = 10/15 = 24/36 = 50/75 = 38/57 = 2/3 = k#

In INVERSE proportion, find the constant by MULTIPLYING the matching quantities:

#2xx30 = 5xx12 = 15xx4 = 3xx20 =10xx6= 60 =k#

If you call the two quantities #x and y#, then we have:

Direct proportion: #k = x/y#

Inverse proportion: #x xx y = k#

Hope this helps.