Shell use 13 cups of oatmeal
Mary should make sure to choose a bank that is FDIC insured. Furthermore, if she has more than maximum deposit insurance amount to deposit, she should spread her deposits out among several separate banks. These should be totally different banks, not simply different branches of the same bank. The FDIC will insure up to the maximum deposit insurance amount at each bank, even if the bank fails.
The given values are:
p = 22% = 0.22
Zc = 1.645 at 90% confidence level.
margin of error, E = 0.04
The formula we can use here is:
E = sqrt(pq/n) * Zc
0.04 = sqrt(0.22*(1-0.22)/n)*1.645
n = (0.22*(1-0.22))*(1.645/0.04)^2
n = 290.22
hence minimum sample size = 290