Problema Solution
A college student earned $8900 during the summer vacation while working as a waiter in a popular resturant. The student invested part of the money at 10% and the rest at 7%. If the student received a total of $704 in interest at the end of the year, how much was invested at 10%.
Answer provided by our tutors
Suppose, the student invested $x at 10% interest and rest of the money $(8900-x) at 7% interest.
Interest of $x (@10%) after 1 year is $(10x/100) = $x/10.
Interest of $(8900-x) (@7%) after 1 year is $(7(8900-x)/100) .
Therefore, total interest after 1 year is $(x/10+7(8900-x)/100).
By the given condition,
x/10+7(8900-x)/100=704,
or, 10x+7(8900-x)=70400,
or, 3x=70400-62300=8100,
or, x=2700.
Thus, he was invested $2700 at 10% interest.