SOLUTION: Hi In January David spent $850 of his income and saved the rest. In February he increased his spending by 20% and his savings decreased by 40%. What was his average savings for th

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Question 1176368: Hi
In January David spent $850 of his income and saved the rest. In February he increased his spending by 20% and his savings decreased by 40%. What was his average savings for the 2 months
Thanks
Answer by Theo(13342) About Me  (Show Source):
You can put this solution on YOUR website!
x = amount that he saved.

in january, he spent 850 and saved x.

in february, he spent 850 * 1.2 and saved .6 * x

let y equal his income.

you get two equations that need to be solved simultaneously.

they are:

y = x + 850
y = .6x + 850 * 1.2

simplify to get:

y = x + 850
y = .6x + 1020

subtract the second equation from the first to get:

0 = .4x - 170

add 170 to both sides of the equation and switch sides to get:

.4x = 170

solve for x to get:

x = 170 / .4 = 425

your original two equations become:

y = 425 + 850 = 1275
y = .6 * 425 + 1.2 * 850 = 255 + 1020 = 1275

he saved 425 in january and .6 * 425 = 255 in february for a total of 680.

his average savings for each of the two months was 680 / 2 = 340 per month.