SOLUTION: A woman invested 4 times as much at 3% as she did at 6%. The total amount of interest she earns in 1 year from both accounts is $1,620. How much did she invest at each rate?

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Question 1152544: A woman invested 4 times as much at 3% as she did at 6%. The total amount of interest she earns in 1 year from both accounts is $1,620. How much did she invest at each rate?
Found 2 solutions by VFBundy, greenestamps:
Answer by VFBundy(438) About Me  (Show Source):
You can put this solution on YOUR website!
3% account:
Principal = 4p
Rate = 0.03
Interest = 4p * 0.03 = 0.12p

6% account:
Principal = p
Rate = 0.06
Interest = p * 0.06 = 0.06p

0.12p + 0.06p = 1620

0.18p = 1620

p = 9000

3% account:
Principal = 4p = $36,000

6% account:
Principal = p = $9000

Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


Here is an unorthodox way of solving the problem that works for me....

(1) Determine the average interest rate, given that 4 times as much was invested at 3% as at 6%:

%284%28.03%29%2B1%28.06%29%29%2F5+=+0.036

(2) Determine the total amount invested, given the interest of $1620 and knowing the average interest rate:

0.036%28x%29+=+1620
x+=+1620%2F0.036+=+45000

(3) Divide the total of $45,000 in the ratio 4:1

ANSWER: $36,000 at 3%; $9000 at 6%

CHECK: .03(36000)+.06(9000) = 1080+540 = 1620