Find two consecutive natural numbers whose product is 20.

Question

Philoid · Accepted Answer

Let the consecutive numbers be a, a + 1.

⇒ a(a + 1) = 20

⇒ a² + a – 20 = 0

⇒ a² + 5a – 4a – 20 = 0

⇒ a(a + 5) – 4(a + 5) = 0

⇒ (a – 4)(a + 5) = 0

⇒ a = 4 as a is a natural number

Thus the numbers are 4 and 5.