Question

If x varies directly as y, and x = 10 when y = 5, find x when y = 9. x = ______

Answer 1

Since x varies directly as y, consider the following diagram:

by cross-multiplication, we get:

`5x\text{ = (9)(10)}`

this is equivalent to:

`5x\text{ = 90}`

solving for x, we get:

`x\text{ = }(90)/(5)=18`

so that, we can conclude that the correct answer is:

x = 18.