SOLUTION: Hi.. My son is in fifth grade and has this problem we can't solve. Leslie has 10 gift cards . Some are square in shape and some are triangular . The cards have 34 side

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Question 953068: Hi.. My son is in fifth grade and has this problem we can't solve. Leslie has 10 gift cards . Some are square in shape and some are triangular . The cards have 34 sides altogether. How many square cards does she have?
Thank you for your help!
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

Leslie has 10 gift cards .
Some are SQUARE in shape => these have 4 sides
and some are TRIANGULAR => these have 3 sides

let SQUARE be x and TRIANGULARbe y:
if Leslie has 10 gift cards, means x%2By=10....eq.1
if the cards have 34 sides altogether, means 4x%2B3y=34...eq.2
now we have a system to solve:
x%2By=10....eq.1
4x%2B3y=34...eq.2
----------------------------
x%2By=10....eq.1...solve for x
x=10-y.........substitute in eq.2
4%2810-y%29%2B3y=34...eq.2..solve for y
40-4y%2B3y=34
40-y=34
40-y%2By=34%2By
40=34%2By
40-34=y
highlight%28y=6%29
now find x:
x=10-y
x=10-6
highlight%28x=4%29
so, Leslie has 4 square cards