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September 28th, 2019, 07:32 PM   #1
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How much was invested?

Here's a question I cannot figure out. It's multiple-choice:

A total of 15K was invested in accounts earning 6 percent annual simple interest and in bonds earning 10 percent annual simple interest. If twice as much of the 15K had been invested in bonds, the earnings would have been 160 dollars higher. How much was invested in bonds?

a) 4,000
b) 7,000
c) 8,000
d) 11,000

Please help me understand how to do this, step-by-step, not just give me the answer. Thank you!

Last edited by mjsilverfly; September 28th, 2019 at 07:34 PM.
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September 29th, 2019, 03:51 AM   #2
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$E = \text{ earnings in thousands}$

$x = \text{ amount invested in bonds at 10% in thousands}$

$E = x(0.10) + (15-x)(0.06)$

double the bond investment ...

$E+0.160 =2x(0.10) + (15-2x)(0.06)$

subtracting the first equation from the second, term for term ...

$0.160 = x(0.10) - x(0.06) \implies x = \dfrac{0.160}{0.04} = 4$
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