**Question:**Bob invested $20,000, part at 14% and part at 13%. If the total interest at the end of the year is $2,720, how much did he invest at 14%?

**Answers:**

Use this chart that I've made fora nearly identical problem.

http://www.flickr.com/photos/18955982@n0...

a+b=20,000 -> b=20,000 - a (substitute this for b)

.14a+.13b=2720

.14a+.13(20,000 - a) = 2720

solve for a

.14a+2600 - .13a=2720

.01a+2600=2720

.01a=120

solve

you do 0.14x+0.13(20000-x)=2720

solve.

0.14x+2600-0.13x=2720

simplify and add like terms.

0.01x+2600=2720

minus 2600 from both sides (simplify)

0.01x=120

x=12000

Bob invested $12,000 at 14% and $8,000 at 13%

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