A varies jointly with B and C. A = 6 when B = 3 and C = 2. Find A when B = 5 and C = 7.

17.5 35 105 70

35

When A varies jointly with B and C A = kBC,   where k is a constant  A = 6, B = 3, C = 2  Then, 6 = k.6   ⇒     k = 1     Now, when B = 5 and C = 7 A = kBC   ⇒ A = 1.5.7  ⇒ A = 35