Answered

Carlos invested part of $3,000 in a 10% certificate account and the rest in a 6% passbook account. The total annual interest from both accounts is $270. How much did he invest at 6%?



Answer :

(3000-n)*(10/100)+n*(6/100) = 270
300 - 0.1n + 0.06n = 270
300 - (0.1n - 0.6n) = 270
300 - 0.04n = 270
-0.04n = -30
n = -30/-0.04 = 750
Investment at 6% = 750
Investment at 10% = 3000 - 750 = 2250
And to check just plug it back in so,
(0.06*750)+(0.1*2250) = 270