Edward C. answered • 03/23/15

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Let X = amount invested at 7.5%

Then 12000 - X = amount invested at 5%

Total interest was $775 ==> 0.075*X + 0.05*(12000 - X) = 775

0.075*X + 600 - 0.05*X = 775

0.025*X = 175

X = 175 / 0.025 = 7000

So $7000 was invested at 7.5% and $5000 was invested at 5%

Check: 7000*0.075 + 5000*0.05 = 525 + 250 = $775