Question

If d varies directly as t, and if d=4 when t=9, find d when t=21

Answer 1

Here we are given that d varies directly as t.

This means that d is directly proportional to t.


So, we can write:

$d = kt$

where k is a constant. 

We have been given that d = 4 when t = 9. We can put these values and find our constant.

$d = kt \\ \\ \implies 4 = k \times 9 \\ \\ \implies k =\frac{4}{9}$

Thus, our equation becomes:
$d = kt \\ \\ \\ \implies \boxed{d = \frac{4}{9} t}$


Now, we are asked to find value of d when t = 21. 

$d = \frac{4}{9} t \\ \\ \\ \implies d = \frac{4}{9} \times 21 \\ \\ \\ \implies d = \frac{4}{3} \times 7 \\ \\ \\ \implies \boxed{d = \frac{28}{3}}$


Thus, when t = 21, the value of d is $\frac{28}{3}$


Hope it helps
Purva
Brainly Community