Question

I lay aside each month $20 more than I lay aside the month starting with $100 in the 1st month. How many months will it take me to lay aside a total of 5,800?

Answer 1

It is an AP with first term 100 and common difference 20

use formula

Sum=n/2(2*first term+(n-1)*common difference)

Your answer would come out to be 19 months or 1 year and 7 months.