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%?

Answer 1

$4000

I'm not sure how the backstory affects the calculations, but Kudos to you, fictional Walt, for managing to work two jobs and save for the future at that rate. Where are you finding those kinds 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 #

By multiplying the first equation by.08 and subtracting the second, we can find the value of x.

#.08 x + .08 y = 800#

#.01 x = 40 #

#x = 4000 #

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

Verify:

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

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Answer 2

Eli Assouline

$4,000 was invested at 7%.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.