Question

y varies directly as x and inversely as the square of z. y = 65 when x = 80 and z=4. Find y when x= 18 and z=3.

Answer 1

Answer: y

=

18

Explanation:

As

y

varies directly as

x

, we have

y

∝

x

. Also it varies inversely as square of

z

, which means

y

∝

1

z

2

.

Hence,

y

∝

x

z

2

or

y

=

k

×

x

z

2

, where

k

is a constant.

Now when

x

=

80

and

z

=

4

,

y

=

10

, so

10

=

k

×

80

4

2

=

k

×

80

16

=

5

k

Hence

k

=

10

5

=

2

and

y

=

2

x

z

2

.

So when

x

=

36

and

z

=

2

,

y

=

2

×

36

2

2

=

72

4

=

18

Step-by-step explanation: