SOLUTION: I am 4 times older than my brother. In 2 years time I will be just 3 times his age. In how many years will my brother be 1/2 my age?

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Question 807886: I am 4 times older than my brother. In 2 years time I will be just 3 times his age. In how many years will my brother be 1/2 my age?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +m+ = my age now
Let +b+ = my brother's age now
+m+%2B+2+ = my age in 2 years
+b+%2B+2+ = my brother's age in 2 years
Let +n+ = the number of years from now
when my brother will be 1/2 my age
+b+%2B+n+ = my age in +n+ years
+m+%2B+n+ = my brother's age in +n+ years
---------------------------------
(1) +m+=+4b+
(2) +m+%2B+2+=+3%2A%28+b+%2B+2+%29+
(3) +b+%2B+n+=+%281%2F2%29%2A%28+m+%2B+n+%29+
----------------------------
This is 3 equations and 3 unknowns, so it's solvable
Substitute (1) into (2)
(2) +4b+%2B+2+=+3b+%2B+6+
(2) +b+=+4+
and, since
(1) +m+=+4b+
(1) +m+=+16+
and
(3) +b+%2B+n+=+%281%2F2%29%2A%28+m+%2B+n+%29+
(3) +4+%2B+n+=+%281%2F2%29%2A%28+16+%2B+n+%29+
(3) +8+%2B+2n+=+16+%2B+n+
(3) +n+=+8+
---------------
In 8 years will my brother be 1/2 my age
check:
In 8 yrs I will be +16+%2B+8+=+24+
In 8 yrs my brother will be +4+%2B+8+=+12+
He is half my age
OK