Question

Jimmy's dad gave him 100$ on his birthday which is January 1st. Jimmy deposited the 100$ in his savings account the same day. At the beginning of every month thereafter Jimmy decides to deposit three times the amount he did in the previous month. on June 15th of the same year, what will be the amount in Jimmy's account

Answer 1

Assuming that no compounding happens from January to June, then no interest is added to the savings account.

a1 = 100
r = 3

Sn = a1 (1 - r^n) / (1 - r)
S5 = 100 (1 - 5^5) / (1 -5)
S5 = $78,100

On June 15th, there will be $78,100 on his account.