Step-2

Title: Normal distribution

Grade: 9-a Lesson: S4-L9

Explanation: Hello Students, time to practice and review the steps for the problem.

Step Type Explanation Answer

1

Problem

For a certain type of computers, the length of time bewteen charges of the battery is normally distributed with a mean of 50 hours and a standard deviation of 15 hours. John owns one of these computers and wants to know the probability that the length of time will be between 50 and 70 hours.

2

Formula:

\$Z = (X-\mu )/ \sigma\$

3

Step

From the given data

\$\mu = 50 , \sigma = 15 , X_1 = 50, X_2 = 70\$

4

Clue

Probability that the length of time will be between 50 and 70 hours.

P(50<X<70)

5

Step

Converting to standard normal curve

\$P(50<X<70) = (50-50)/ 15 < P((X-\mu )/ \sigma) < (70-50)/ 15)\$

\$P(50<X<70) = P(0<Z<1.33)\$

6

Step

P(0<Z<1.33)

[area to the left of z=1.33] - [area to the left of z=0]

7

Hint

Take the values from the standard normal distribution table or chart

8

Step

P(0<Z<1.33)

0.9082 - 0.5

9

Step

P(0<Z<1.33)

0.4082

10

Step

Probability that the length of time will be between 50 and 70 hours

0.4082

11

Answer

B

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