Question 377901: The sum of three numbers is 18. The sum of the first and second number is 15, and the first number is 3 times the third number. Find the numbers
Found 3 solutions by richard1234, mananth, sophxmai:
Answer by richard1234(7193)   (Show Source):
You can put this solution on YOUR website! Suppose these three numbers are a, b, and c. We can write the following equations:
#1 a+b+c = 18
#2 a+b = 15
#3 a = 3c
If we subtract #2 from #1 we have c = 3. From #3 we have a = 3(3) = 9. Finally, since a+b+c = 18 we plug in our known values for a and c to obtain b = 6. Therefore our three numbers are a = 9, b = 6, c = 3.
Answer by mananth(16946)  (Show Source):
Answer by sophxmai(62)  (Show Source):
You can put this solution on YOUR website! x+y+z=18 <--First equation
x+y=15 <--Second equation
x=3z <--Third equation
Subtract second equation from the first one.
x+y+z=18
x+y=15
z=3
Substitute z=3 into the third equation.
x=3z
x=3(3)
x=9
Substitute x=9 into the second equation.
x+y=15
(9)+y=15
y=6
Numbers are 9, 6, and 3
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