Mardi received an inheritance of $40,000. She invested part at 9% and the rest at 12%. Her total annual income from the investments was $3900. Find the amount she invested at 9%

She invested $30,000 at 9%

Step-by-step explanation:

Let the amount invested per percentage be $x and $y respectively

Total investment is 40,000

This means that;

x + y = 40,000 ••••••••••(i)

Now for her income;

9/100 * x = 9x/100

for the 12% = 12/100 * y = 12y/100

Now;

9x/100 + 12y/100 = 3,900

9x + 12y = 390000 •••••••••(ii)

we solve both simultaneously

From i, y = 40,000-x

Substitute this into ii

9x + 12(40,000-x) = 390,000

9x + 480,000-12x = 390,000

3x = 480,000-390,0000

3x = 90,000

x = 90,000/3

x = $30,000

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