A person has 2 parents, 4 grandparents, 8 great grand parents, and so on. Find the number of his ancestors during the ten generations preceding his own.

Question

Philoid · Accepted Answer

The number of ancestors are 2, 4, 8, 16....it is in GP
common ratio = r
a = 2
and n = 10
Sum of GP for n terms

⇒ a = 2, r = 2, n = 10

∴ Substituting the above values in (1) we get

⇒

⇒ 2(1024 - 1)

⇒ 2(1023)

⇒ 2046