Question

Lana finished the race in 13.2 seconds . If 84 other girls ran in the event, approximately how many runners did she beat?

Answer 1

Complete question :

The 100m dah times in the girl's track meet were normally distributed with a mean of 13 seconds and a standard deviation of 0.3 seconds.

Lana finished the race in 13.2 seconds . If 84 other girls ran in the event, approximately how many runners did she beat?

Answer:

21 runners

Step-by-step explanation:

Mean, μ = 13 seconds

Standard deviation, σ = 0.3

Lana's race time = 13.2

We find the proportion of runners who had race time above 13.2 ;

Proportion of who had race tune above 13.2

P(x > 13.2)

Obtain the Zscore

Zscore = (x - μ) / σ

Z = (13.2 - 13) / 0.3

Zscore = 0.2 / 0.3 = 0.6667

P(Z > 0.6667) = 0.25239 (Z probability calculator)

This is about 0.25239 * 100 = 25.24% = 25% (nearest percent)

Hence, Number of runners Lana beat = 25% of total runners ;

0.25 * 84 = 21

Hence, Lana beat about 21 runners