Question

Suppose y varies directly with x, and y= 7 when x = 3. What is the value of x when y = 28? If 7 = k(3) then 28 = k(x) Find x

Answer 1

Let y and x be the numbers that  varies directly (that means they keep the same proportion)

Then we have 7y = 3x, OR y/x =7/3 (this ratio should be kept for any value of x and y:
y/x = 7/3, if y = 28, then 28/x = 7/3 or x = (3)(28)/7 = 12

SO X = 12