문제

How many numbers are in the series 0, 5, 10, 15, …, 100?

tn = a + (n - 1) × d

공식을 사용하여 문제를 푼다

100 = 0 + (n - 1) x 5

n = 21

책의 답

There are 21 terms in the series. If you said 20, you just

experienced a fencepost error (not knowing whether to count the fenceposts or the spaces between them).