W varies jointly as x and p. If w=78 when x=2 and p=10, find x when w=858 and p=5.5

W=kxp

where

k is the constant of proportionality given by:

k=w/xp

If w=78 when x=2 and p=10 then

k=78 / (2*10)

k=3.9

thus the formula is:

w=3.9xp

b] find x when w=858 and p=5.5

plugging the values in the formula we get:

858=3.9 * 5.5*x

hence

x=858 / (3.9*5.5)

x=358/21.45

x=16.69