Question

The mean of the data set is 40 and one standard deviation is 5. About what percent of the numbers fall between 35 and 50?

53.2%
68.2%
77.4%
81.8%

Answer 1

The correct option is D. 81.8%

Explanation:

Mean of the data set is given to be 40

⇒ μ = 40

Standard deviation of the data set is given to be 5

⇒ σ = 5

Now we are supposed to find out what percent of the numbers fall between 35 and 50

`\implies z =(x-\mu)/(\sigma)`

Now for P(35 < x < 50) :

Substitute x = 35 ⇒ z = -1

Substitute x = 50 ⇒ z = 2

So, P(-1 < z < 2) = P(z < 2) - P(z < -1)

⇒ P(-1 < z < 2) = 0.9772 - 0.1587

⇒ P(-1 < z < 2) = 0.8185

⇒ P(-1 < z < 2) = 81.8%

Therefore, 81.8% percent of the numbers fall between 35 and 50

Hence, The correct option is D. 81.8%