Question

On Dolores's tenth birthday her grandfather deposited $35

in a savings account for her. Each year, her grandfather
deposited twice the amount of the previous year's deposit.
How much money did her grandfather deposit on Dolores's
eighteenth birthday?

Answer 1

8960

Explanation:

Answer 2

Answer: Her grandfather deposited $4480 on Dolores's eighteenth birthday.

Explanation:

Initial amount deposited = $35 (on tenth birthday)

Amount deposited after a year = 2 x ($35) (on eleventh birthday)

Amount deposited after 2 years =2 x( 2 x ($35)) = 2²(35)(on eleventh birthday)

It is following the geometric progression, where a= 35, r= 2 (common ratio)

nth term in GP =
`ar^(n-1)`

Amount deposited on eighteenth birthday (i.e. n=8) =
`(35)(2)^(8-1)`

`=35*2^7=35*128=4480`

Hence, Her grandfather deposited $4480 on Dolores's eighteenth birthday.