Question

if x and y vary inversly and x=25 when y=3.find y, when x=15​

Answer 1

when x= 25 then y= 3.

when x = 15 then y= ?

since x and y vary inversely, that means if x increases then y decreases and vice versa.

so,

$y = \frac{25}{15} \times 3 \\ y = \frac{25}{5} \\ y = 5$

when x = 15 then y = 5

Answer 2

The solution is done below :

  Given, x and y vary inversely

  i.e., x ∝ $\frac{1}{y}$

If k be variation constant, we can write

  x = $\frac{k}{y}$

  ⇒ k = xy .....(i)

When x = 25 and y = 3, from (i), we get

  k = 25 * 3

  ⇒ k = 75

Now, we need to find the value of y when x = 15. Putting x = 15 and k = 75 in (i), we get

  75 = 15 * y

  ⇒ y = $\frac{75}{15}$

  ⇒ y = 5 ,

which is the required value of y when x = 15 for x varying y inversely.