Principal and amount invested

Question

Tom invested part of $12,000 in a 5% simple interest account and the remainder in 7.5% simple interest account. If the total interest earned from the two investments in one year was $775, how much was invested in each account?

Answer 1

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