SOLUTION: Peter is 12 years older than his brother David. If four times Peter�s age plus two times David�s age is 66, how old are Peter and David?

Question 392388: Peter is 12 years older than his brother David. If
four times Peter�s age plus two times David�s age
is 66, how old are Peter and David?
Answer by fafa(13) (Show Source): You can put this solution on YOUR website!
peter=P
david=D
first formula is P=12+D (because peter is 12 years older thn David)
the second formula is 4P+2D=66 (because four times Peter�s age plus two times David�s age is 66)
and then we substitute the first formula to the second formula
4P + 2D = 66
4(12+D) + 2D = 66
48 + 4D + 2D = 66
48 + 6D = 66
48 - 48 + 6D = 66 - 48
6D=18
6D : 6 = 18:6
D= 3
so David is 3 years old
P = 12 + D
P = 12 + 3
P = 15
so peter is 15 years old
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