Question

Last year Anne invested a total of $6,400. She invested part of it in a certificate of deposit that earned 2% interest for the year. The rest of the investment was put into bonds that earned 6% interest for the year. Anne earned 3.75% in interest overall. How much money did Anne put into each type of investment?

Answer 1

Suppose Anne invested $x in certificate of deposit and $(6400-x) in bonds.
Interest rate earned in certificate deposit will be:
2/100*x=0.02x
Interest earned in bonds will be:
6/100*(6400-x)
=(364-0.06x)
Total amount of interest earned was 3.75%, this is equal to:
3.75/100*6400
=240
hence we conclude that:
0.02x+(364-0.06x)=240
0.02x+364-0.06x=240
0.02x-0.06x=240-364
-0.04x=-124
x=-124/(-0.04)
x=$3100
hence the amount invested in certificate was $3100 and the amount invested in bonds was (6400-3100)=$3300