Y varies directly with x. If y = 21, when x = 7, find y when x = 28.

y = - 4.98

Step-by-step explanation: This statement means

y

∝

x

, which can also be written in the form

y

=

k

x

when it is directly proportionate and

y

=

k

x

when inversely proportionate, where

k

is a value we need to work out. Since the equation is in the form

y

=

k

x

we know that...

21

=

K

×

7

∴

k

=

21

7

=

3

.

So we can write this as the formula:

y

=

3

x

Therefore using the value of

x

=

−

1.66

y

=

3

x

→

y

=

3

×

−

1.66

=

−

4.98

step-by-step explanation:

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