CAT 2017 Quantitative Ability

If a+b + c + d is constant, then the product abed is maximum when a = b =c =d,
(a + 1) = (b + 1) = (c + 1) = (d + 1)
Given that(a + 1) + (b + 1) + (c + 1) + (d + 1) = 8
∴ 4(a + 1) = 8
⇒ (a + 1) = 2∴ Maximum value = 2x2x2x2 = 16