The expenses of customers follows a normal distribution with mean equals to $428, and standard deviation equals to $100. A customer spending $600 or more will receive a gift. If the probability of the shopping centre giving out gifts is at least 0.99, find the smallest no. of customers visiting the store.(adsbygoogle = window.adsbygoogle || []).push({});

My solution is something like:

X: expenses of customers

X~N(428, 100)

P(X>= 600)

= P(Z>= (600-428)/100 )

= P(Z>= 1.72)

= 0.5 - A(1.72)

From the table, P(X>= 600) = 0.5 - 0.4573= 0.0427

n: no. of customers

0.0427^n >= 0.99 <----Why isnt this expression incorrect?

There is another expression (1-0.0427)^n <= 0.01, which is correct. But as far as i'm concerned, they should be both correct Please help!

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: No. of customers (probability)

**Physics Forums | Science Articles, Homework Help, Discussion**