4 Suzette ran 240 yards in the first minute 235 yards in the

4. Suzette ran 240 yards in the first minute, 235 yards in the second minute, 230 yards in the third minute, and so on. How far did Suzette run in 15 minutes?

Solution

1st minute = 240

2nd minute = 235

3rd minute = 230

there is arithmetic progression in suzette running

a1 = 240

common difference d = -5

hence, nth term of arithmetic progression is given by

an = a1 + (n-1)d

an = 240 + (n-1)*-5

to calculate how far did suzette run in 15 minutes plug n = 15

a15 = 240 + (15-1)*-5

a15 = 240 - 70 = 170

therefore, suzette ran 170 yards in 15th minutes

total she ran = 15( 240+170)/2 = 3075 yards