Question

A company is testing a product which is intended to make hair grow faster. One of the test subjects started with a hair length of 8.2 inches. After a year of using the product, the test subject's hair measured 18.4 inches. If the growth rate was constant during the trial period, which of the following statements applies?

1. An additional month of product use is associated with an additional 2.22 inches of growth.
2. An additional 0.85 month of product use is associated with an additional inch of growth.
3. An additional month of product use is associated with an additional 0.85 inch of growth.
4. An additional 2.22 months of product use is associated with an additional inch of growth.

Answer 1

3. An additional month of product use is associated with an additional 0.85 inch of growth.

Explanation:

Given that a company is testing a product which is intended to make hair grow faster. One of the test subjects started with a hair length of 8.2 inches

After a year of using the product, the test subject's hair measured 18.4 inches. If the growth rate was constant during the trial period, then we find that for 12 months hair growth is 10.2 inches

Assuming constant growth for 1 month growth is 10.2/12 = 0.85 inches

i.e. for every month additional use the growth would be 0.85 inches.

The equation relating hair growth and months would be

Hair size = No of months used *0.85 + 8.2

So correct option is

3. An additional month of product use is associated with an additional 0.85 inch of growth.