If a + b=ab and a, b are natural numbers then how many pairs of (a, b) are there?
Answer: 1 pair – (2, 2)
Explanation
a + b = ab
ab – a – b = 0
ab – a – b + 1 = 1
(a – 1)(b – 1) = 1
Now, for this to be true, given that a and b are natural numbers a – 1 = b – 1 = 1.
i.e., 1 x 1 = 1
Therefore, a = 2 and b = 2.