Question

They work-infested $18,000 into accounts, one yielding 4% interest and the other yielding 12%. If he received a total of $1,280 and interest at the end of the year, how much did he invest at 4%?​

Answer 1

$11,000

Explanation:

Let amount invested for 12% yield be p . Amount for 4% yield is therefore (18000-p)

Interest for 12%: 12% of p=0.12p

Interest for 4%: 4% of (18000-p)=0.04(18000-p)=720-0.04p

Total interest:

=0.12p + (720-0.04p)

=0.12p-0.04p+720

=0.08p+720

But we already know the total interest is 1280

Therefore: 0.08p+720=1280

0.08p=1280-720

0.08p=560

p=560÷0.08

p=7000

Therefore at 4% the person invested:

(18000-p)

18000-7000

$11,000