How much do you save after 20 weeks?

Question

Each week you deposit money in a savings account. The first week you deposit $100 in the account. Each week you deposit $1 more than you deposited the week before.

Answer 1

100 + 101 + 102 + 103 + ... 118 + 119 = $2190

1st week 100

20th week 119

100

sum of 101+119 = 220

102+118 = 220

103 + 117 = 220

104+116 = 220

...

109 + 111 = 220

110 =110

sum = 100 + 9(220) + 110 = 210 + 1980 = $2,190