p/q + q/p = (p2 + q2)/pq
Apply the formula of algebra
a 2+ b2 = (a + b)2 - 2ab
p/q + q/p = ( (p + q)2 - 2pq ) / pq
By substituting the pq and p + q values in given equation.
p/q + q/p = ( (p + q)2 - 2pq ) / pq
p/q + q/p = ((10)2 - 2 x 5 ) / 5
p/q + q/p = (100 - 10 )/ 5 = 90/5 = 18
p/q + q/p = 90/5 = 18
p/q + q/p = 18