SOLUTION: Susan invests 3 times as much money at 11% as she does at 7%. If her total interest after 1 year is $2400, how much does she have invested at each rate?

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Question 1102815: Susan invests
3 times as much money at
11% as she does at
7%. If her total interest after
1 year is
$2400, how much does she have invested at each rate?
Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


Let x be the amount invested at 7%; then the amount invested at 11% is 3x.

The interest from the first investment is then .07 times x; the interest from the second is .11 times 3x.

Since the total interest is $2400,
.07%28x%29%2B.11%283x%29+=+2400
.07x%2B.33x+=+2400
.40x+=+2400
x+=+2400%2F.40+=+6000

She invested x = $6000 at 7% and 3x = $18000 at 11%.

CHECK:
.07%286000%29%2B.11%2818000%29+=+420%2B1980+=+2400