Question 884197
"If I collect $1 and $2 coins until I have 275 coins and I have a total of $402 how many $2 coins do I have?"
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Let x = number of $1 coins
and y = number of $2 coins
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From:"collect $1 and $2 coins until I have 275 coins" we get:
x + y = 275
From:"I have a total of $402" we get:
x + 2y = 402
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Simultaneous equations:
x + y = 275
x + 2y = 402
.
multiply top equaion by -1 and ADD to bottom equation:
-x -  y = -275
 x + 2y = 402
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     y = 127 (number of $2 coins)
.
number of $1 coins:
x + y = 275
x + 127 = 275
x = 275 - 127
x = 148