Direct Proportion

If two quantities increase at the same rate so

that if one is doubled so is the other, then the 8

quantities are said to be directly proportional.

In the example shown, if C is the cost of an 7

ice cream and N is the number bought, we

6

write C N (C is proportional to N).

If two quantities are directly proportional 5

then their points lie on a straight line from Cost (£)

the origin. In our example the equation of 4

this line is C = kN for some value of k. k is Three ice creams

called the constant of proportionality and cost three times as

3 much as one etc.

has a value of 1.5 here.

2 Two ice creams cost

Eddie's Ices twice as much as one.

All £1.50 1

1 2 3 4 5

Number of Ice Creams…read more

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