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

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

Step-by-step 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) = $(35)(2)^{8-1}$

$=35\times2^7=35\times128=4480$

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