Question 1161595: Amanda made an extra $70,00 last year from a part time job. She invested part of the money at 10% and the rest at 7%. She made a total of $6400 in interest. How much was invested at 7%
Answer by greenestamps(13209)   (Show Source):
You can put this solution on YOUR website!
(1) A traditional algebraic setup for solving....
x = amount at 10%
70000-x = amount at 7%
10% of x, plus 7% of (70000-x), equals 6400:
Solve using basic algebra....
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(2) A quick and easy way to solve a 2-part "mixture" problem like this, if an algebraic solution is not required....
(1) All $70,000 invested at 10% would yield $7000 interest; all at 7% would yield $4900 interest.
(2) The actual interest, $6400, is 5/7 of the way from $4900 to $7000. ($4900 to $7000 is a difference of $2100; $4900 to $6400 is a difference of $1500; 1500/2100 = 5/7)
(3) That means 5/7 of the total was invested at the higher rate.
ANSWER: 5/7 of $70,000, or $50,000, at 10%; the other $20,000 at 7%.
CHECK:
.10(50000) + .07(20000) = 5000+1400 = 6400
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