Sally kept 400 in her bank account for one year and nine months how much interest did she make if her bank pays 21/2%annual interest?
21÷12=1.75or7/4
400×0.025×1.75=17.50?
Your interest of 21/2% might be a typo.
if you meant 2 1/2 % or 2.5 %,
I = PRT
= 400(.025)(21/12) = 17.5 , which is what you had, so it was a typo
The way you typed it
21/2%
= 10.5%
Interest = 400(.105)(21/12) = 73.5