Question 252188: Crystallina spent her entire $ 20 weekly allowance on books and candy last week. This week she did the same, but she spent 50 % more on candy and 12.5 % less on books.How much did she spend on candy this week?
Answer by drk(1908)   (Show Source):
You can put this solution on YOUR website! This question requires you to set up a system of equations. Let B = books, and C = candy.
The first sentence becomes: 20 = B + C.
50% more than means 100% last week + 50% this week or 150%, which is 3/2
12.5% less than means 100% last week - 12.5% this week or 87.5% which is 7/8.
The second sentence becomes: 20 = (7/8)B + (3/2)C
multiplying the second equation by 8, we get: 160 = 7B + 12C.
Now we have
20 = B + C
160 = 7B + 12C
step 1 - multiply the first equation by -7. This gives us
-140 = -7B -7C
160 = 7B + 12C
step 2 - add down to get
20 = 5C
step 3 - solve for C. C = 4. She spent $4 on candy LAST week. This week, it was $6.
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