The annual sales of romance novels follow the normal distribution. However, the mean and the standard deviation are unknown. Forty percent of the time, sales are more than 470,000, and 10% of the time, sales are more than 500,000. What are the mean and the standard deviation?

Mean(m) = 462,536

sd = 29,268.29

Step-by-step explanation:

Given the following:

P(sales > 470,000) = 40% = 0.4

P(sales > 500,000) = 10% = 0.1

Using the z - table, we can locate the corresponding P values

Z = 1 - p = 1 - 0.4 = 0.6; 1 - 0.1 = 0.9

Locating the closest value to 0.6 on the z table ;

(0.25 + 0.26) / 2 = 0.255

Locating the closest value to 0.9 on the z table ;

Z = 1.28

Recall;

z =( x - m) / sd

Where m = mean ; sd = standard deviation

First condition:

0.255 = (470,000 - m) / sd

0.255 × sd = (470,000 - m) - - - - - (1)

1.28 = (500,000 - m) / sd

1.28 × sd = (500,000 - m) - - - - (2)

We can solve for one of the unknowns y subtracting equation (1) FROM 2

1.28sd - 0.255sd = (500,000 - m) - (470000 - m)

1.025sd =500,000 - m - 470000 + m

1.025sd = 30,000

sd = 29,268.29

Substituting the value od SD into (1) or (2)

1.28 × 29,268.29 = 500000 - m

37463.41 = 50000 - m

m = 50000 - 37463.41

Mean(m) = 462,536

false

step-by-step explanation:

false.   two legs of the trapezoid would be congruent, but the other two would not.   were all the legs congruent, then we'd have a square; were the 2 shorter sides congruent and the 2 longer sides also congruent, we'd have a rectangle.