Question 1208045
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First a typical formal algebraic solution....<br>
x = amount invested at 5%
30000-x = amount invested at 8%<br>
The total interest earned was 2100:<br>
{{{.05(x)+.08(30000-x)=2100}}}
{{{.05x+2400-.08x=2100}}}
{{{-.03x=-300}}}
{{{x=300/.03=10000}}}<br>
ANSWERS:
x = p10000 invested at 5%
30000-x = p20000 invested at 8%<br>
And then a fast and easy informal method for solving any 2-part "mixture" problem like this....<br>
2100 interest on an investment of 30000 is an interest rate of 2100/30000 = .07 = 7%
7% is 2/3 of the way from 5% to 8% (look at the three numbers 5, 7, and 8 on a number line if it helps)
That means 2/3 of the total p30000 was invested at the higher rate<br>
ANSWERS:
2/3 of p30000 = p20000 invested at 8%
1/3 of p30000 = p10000 invested at 5%<br>