Question

The average amount my store  members spend on my store each year is normally distributed with
mean $1, 400 and standard deviation $400. Find the probability that a randomly selected my store member
spends between $950 and $1, 625 in a year.

Answer 1

Solution :

Given that ,

mean = = 1400

standard deviation = = 400

P(950 < x < 1625)

= P[(950 - 1400)/ 400) < (x - ) /  < (1625 - 1400) / 400) ]

= P(-1.13 < z < 0.56)

= P(z < 0.56) - P(z < -1.13)

Using z table,

= 0.7123 - 0.1292

= 0.5831

P(950 < x < 1625) = 0.5831

Probability = 0.5831