Q18 of 176 Page 20

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.

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


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