Question 381612
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Hi,         
Let x and (12-x)represent the number of 5's and 10's respectively
Question states***
 5x + 10(12-x) = 115
Solving for x
-5x + 120 = 115
     5 = 5x
     1 = x, the number of fives, number of tens is 11.  (12-1)

CHECKING our Answer***
  $5 + $110 = $115