Question : If the number p is 5 more than q and the sum of the square of p and q is 55, then the product of p and q is:
Option 1: 10
Option 2: –10
Option 3: 15
Option 4: –15
Correct Answer: 15
Solution :
Given: p = q + 5
⇒ p – q = 5
Also, p
2
+ q
2
= 55
⇒ p
2
+ q
2
– 2pq + 2pq = 55
⇒ (p – q)
2
+ 2pq = 55
⇒ 25 + 2pq = 55
⇒ 2pq = 30
$\therefore$ pq = 15
Hence, the correct answer is 15.
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