Question

The fitness center held a weight loss competition in which 128 people participated. The amount of weight loss was normally distributed with a mean of 18 pounds and a standard deviation of 5.4 pounds. Approximately how many people lost at least 15 pounds?

Select one:
a. 72
b. 78
c. 84
d. 90

Answer 1

the answer to this problem is D

Answer 2

d. 90

Explanation:

z = (x - mean)/SD = (15 - 18)/5.4 = - 3/5.4 = -0.55555555... ≈

≈ -0.56

remember the z-table represents the rounded values.

the z-table at -0.56 gives us the p-value of 0.28774.

that is the probability to the left of 15 pounds, so, the probability to have lost 15 pounds or less.

to have lost at least 15 pounds, we have to get the right side of 15 pounds in the bell curve.

and that is 1 - 0.28774 = 0.71226

so, the probability to have lost at least 15 pounds is therefore 0.71226.

how many people are that ?

well, there were in total 128 people (with the total probability of 1 representing everything).

the number of people that lost at least 15 pounds are the proportionate share of 0.71226 of 1 (the whole) :

128 × 0.71226 = 91.16928...

so, the closest answer option is d. 90