posted by Bobby Jones .
Determine the equation of combined, then solve for the missing value.
Variation x varies directly with y and z.
x=5 when y=10 and z=5. find x when y=20 and z=10
"x varies directly with y and z" ---> x = k(yz), where k is a constant
given: when x=5, y = 10 and z = 5
5 = k(10)(5)
50k = 5
k = 1/10
then x = (1/10)yz
for y=20, z=10
x = (1/10)(20(10) = 20