Question

If z varies jointly as x and y and inversely as w^2?, and

z = 72 when x = 80, y = 30 and
w=5, then find z when x = 20, y = 60 and w=9.

Answer 1

Explanation:

z = (k*x*y) / w²

Where,

k = constant of proportionality

z = 72 when x = 80, y = 30 and w = 5

z = (k*x*y) / w²

72 = (k * 80 * 30) / 5²

72 = 2400k / 25

Cross product

72 * 25 = 2400k

1800 = 2,400k

k = 2,400/1800

k = 24/18

= 4/3

k = 1 1/3

k = 1.33

find z when x = 20, y = 60 and w=9

z = (k*x*y) / w²

z = (1.33 * 20 * 60) / 9²

z = (1596) / 81

Cross product

81z = 1596

z = 1596/81

z = 19.703703703703

Approximately,

z = 19.7