Question

A family has two cats named Gordo and Flaco. Gordo weighs 15 pounds and Flaco weighs 8 pounds. A cat’s weight is classified as unhealthy if the weight is located in the top 5% or bottom 5% of all cat weights. The distribution of cat weights is approximately normal with mean 9.5 pounds and standard deviation 1.5 pounds. Which of the following is the best description of Gordo’s and Flaco’s weights?

Answer 1

Gordo's weight = 15 pounds

It is outside the healthy weight range and is in the top 5% of weights of cats.

Gordo's weight makes Gordo unhealthy.

Explanation:

μ = mean weight = 9.5 pounds

σ = standard deviation = 1.5 pounds

This is a normal distribution problem

We first calculate the limit of the bottom 5% of weights

Let the z-score for this limit be z'

P(z < z') = 0.05

From the normal distribution table,

z' = -1.645

And the limit for the top 5% which is z" = 1.645.

The weight that corresponds to these scores are then calculated.

Standardized scores are given as

z = (x - μ)/σ

So,

z' = (limit for the bottom 5% - μ)/σ

-1.645 = (limit for the bottom 5% - 9.5)/1.5

limit of the bottom 5% = (-1.645)(1.5) + 9.5 = 7.033 pounds

z" = ( (limit for the top 5% - μ)/σ

1.645 = (limit for the top 5% - 9.5)/1.5

limit of the bottom 5% = (1.645)(1.5) + 9.5 = 11.968 pounds

Therefore the healthy weight range for cats is (7.033 < x < 9.968)

Gordo's weight = 15 pounds

It is outside the healthy weight range and is in the top 5% of weights of cats.

Gordo's weight makes the cat unhealthy.

Flaco's weight = 8 pounds

Flaco's weight lies in the healthy weight range for cats. Hence, Flaco is a healthy cat.