Walt made an extra $10,000 last year from a part-time job. He invested part of the money at 8% and the rest at 7%. He made a total of $760 in interest. How much was invested at 7%?

1 Answer
Dean R.
May 13, 2018

$4000

Explanation:

Not sure what the backstory adds to the math, but good for you fictional Walt for saving for the future while working two jobs. Where are you getting those kind of rates these days?

We'll call #x# the amount invested at 7% and #y# the amount invested at 8%.

#x + y = 10000#

#.07 x + .08y = 760 #

We solve for x by multiplying the first equation by .08 and subtracting the second.

#.08 x + .08 y = 800#

#.01 x = 40 #

#x = 4000 #

That's $4000 at 7% and $6000 at 8%.

Check:

#.07 (4000) + .08(6000) = 760 quad sqrt#

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