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Question 953149: Jennifer has $5000 to invest into two accounts paying simple interest. The first account pays a guaranteed 8% simple interest and the second account pays a guaranteed 10% simple interest. How much must Jennifer invest into each account in order to earn $800 combined annual interest on both accounts?
I have been trying elimination and substitution for about 30 minutes and every time I come up with a negative answer which, obviously, is not correct.
I set it up with X being the account offering 8% interest and Y being the account offering 10% interest.
X+Y=5000
.08X+.1Y=800
I tried the following:
-.1x-.1Y=-500
.08X+.1Y=800
-.02X=300
I also tried:
.08X+.1(5000-X)=800
.08X+500-.1X=800
-.02X=300
I cannot figure out where the problem is and I am going insane trying to find it!
Answer by macston(5194)   (Show Source):
You can put this solution on YOUR website! The problem is in the problem itself: $5000 cannot earn $800 per year in interest at the rates given: $800/$5000(100%)=16% so she would have to invest at a minimum of 16% to reach her goal.
PS: The reason you cone up with a negative amount, when you subtract the negative from the total it leaves more money than you have to invest in the other account.
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