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A math problem: There are 30 coins, 1.50 1 yuan each 10, and 15 coins are taken out, which happens to be in 7 yuan. How many pieces do you each take? How to form an equation
Let 1 angle x, 5 angle y and 1 element z, then according to the meaning of the question:

0. 1X+0.5Y+Z=7 ( 1)

X+Y+Z= 15 (2)

X is an integer multiple of 5 (3) (this is easy to understand, money is not an integer unless it is an integer of 5)

According to (1) and (2):

9X+5Y=80

And x can only be an integer multiple of 5.

Then when X=5, Y=7, X= 10 and above, y is negative, then x can only be equal to 5.

Then X=5, Y=7 and Z=3.

So 1.50 1 yuan coins are 5, 7 and 3 respectively.