anonymous 5 years ago can someone give me a formula for this please? A college student earned $8400 during summer vacation working as a waiter in a popular restaurant. Part was invested at 8% simple interest and the remainder at 9% simple interest. At the end of one year, the student had earned$707 interest. How much was invested at 9%

1. Owlfred

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2. anonymous

707=0.08(8400 +0.09(8400)

3. anonymous

not possible

4. amistre64

the formula(s) would be: a + b = 8400; a = 8400-b 707 = a(.08) + b(.09) ; substitue the 'value' of a into this equation and solve for 'b'

5. anonymous

oops yes it is sorry. call the amount invested at 9% x. then \.09x+.08(8400-x)=707\]

6. anonymous

$.09x+.08(8400-x)=707$ $.01x+672=707$ $.01x=35$ $x=\frac{35}{.01}=3500$