[問題]GWD 12-14

[Flory]

In the first week of the year, Nancy saved $1. In each of the next 51 weeks, she saved $1 more than she had saved in the previous week. What was the total amount that Nancy saved during the 52 weeks?

Ans: C. $1378

可否請善心人士提供此題的解題公式?

ps. 因為問題的連結有誤, 所以我找不到這個問題的解答.

Thanks million!

[himax67]

1+2+3+.....+52
=(1+52)*52/2=1378

[Flory]

謝謝himax67的回覆. 可否請教為什麼要除以2?

[huacy]

梯形面積 = (上底+下底)*高/2
所以從 1+2+....+10 一樣也是 (1+10)*10/2 = 55

[Flory]

oh i see. thank you huacy! ^^

[chris8888]

這是等差級數的公式. 我記得好像國中還是高中學過