Question 502309: There are 2 brothers. John is 12 years younger than Mike. In 9 years, John will half Mike's age. How old will John be in 4 years? Answer by Maths68(1474) (Show Source):
You can put this solution on YOUR website! Let
Present age of John = j
Present age of Mike = m
John is 12 years younger than Mike means if subtract 12 from Mike's present age both Mike and John will be of same age
j=m-12...................(1)
In 9 years means we have to add 9 in the present ages of John and Mike
j+9=m+9
then
John will half Mike's age
j+9=(m+9)/2
2(j+9)=m+9
2j+18=m+9
2j=m+9-18
2j=m-9...............(2)
Put the value of j from (1) to (2)
2(m-12)=m-9
2m-24=m-9
2m=m-9+24
2m=m+15
2m-m=15
m=15
Put the value of m in (1)
j=m-12
j=15-12
j=3
Present age of John = 3 years
Present age of Mike = 15 years
How old will John be in 4 years? for this add 4 to his present age = 3+4=7years
