Posted by TUHITUHI on Monday, October 1, 2012 at 10:46am.
here's another answer. These story problems are all basically the same: translate words to symbols and solve the equation(s).
m = 4s
m = 5d
now, we need to figure out how many years from now the son will be 3 times his present age:
3s - s = 2s = m/2
so, adding that many years to mother and daughter, we have
m + m/2 = 2(d+m/2)+3
so, we now have two equations
m = 5d
3/2 m = 2d + m + 3
3/2 (5d) = 2d + 5d + 3
15/2 d = 2d + 5d + 3
d/2 = 3
d = 6
d=6
m=30
s=7.5
in 15 years we will have
s = 22.5
d = 21
m = 45 = 2*21 + 3
Now try some of your other problems, and show us where you get stuck, if you do.
present: let .......
mother ---20 x
son ------ 5x
daughter --4x
What is 3 times son's age ---> 15x
When is son 3 times as old as he is now?
in 15x - 5x years or in 10x years
at that time
son ----- 15x
mother --- 20x + 10x = 30x
daughter -- 4x + 10x = 14x
mother's age = 2 times daughter's age plus 3
30x = 2(14x) + 3
2x = 3
x = 1.5
present ages:
mother -- 30
son ----- 7.5
daughter -- 6
check:
3 times son's present age is 22.5, this will happen in 15 years
at that time ...
mother is 45
son is 15
daughter is 21
is 45 = 2(21) + 3 ??? , YES!!
musa can cut his grass in 7hrs and his brother can also do the same in 3hrs .if both of them do the work the same time,how long will it take them to do the same work?