Question

If D varies directly with t and D is 108 when t is 4, find D when t is 7.

Answer 1

189

Explanation:

Given : D varies directly with t and D is 108 when t is 4

To Find: Find D when t is 7

Solution:

D varies directly with t

D ∝ t

So,
`D=kt`

where k is the constant of proportionality

Now we are given that D is 108 when t is 4

So,
`108=k(4)`

`(108)/(4)=k`

`27=k`

Thus the constant of proportionality i.e. k = 27

So,
`D=27t`

Now substitute t = 7

So,
`D=27(7)`

`D=189`

So, D = 189 when t = 7

Answer 2

D
`\alpha`t
D=kt
108=k(4)
108=4k
k=
`(108)/(4)`
k=27
The equation connecting D and t is;
D=27t
When t=7,
D=27*7
D= 189