Question

Is y varies directly as x, and y is 18 when x is 5 witch expression can be used to find the value of y when x is 11?

Answer 1

As the variation is direct we have:
 $y = k * x$
 Where,
 k: proportionality constant
 We must find the value of k.
 For this we use the following data:
 y is 18 when x is 5.
 Substituting values we have:
 $18 = k * 5$
 From here, let's clear k:
 $k = 18/5 k = 3.6$
 Then, replacing values we have:
 $y = 3.6 * x$
 For x = 11 we have:
 $y = 3.6 * 11 y = 39.6$
 Answer:
 An expression that can be used to find the value of y when x is 11 is:
 $y = 3.6 * x$
 When x = 11 we have:
 $y = 39.6$