Some important points
 Assume the present ages, then proceed with the equations.
 While making equations, always remember to convert both sides into either present year or the given year i.e. time frame should be same.
 5 years ago `to`present year  5 years
 5 years hence `to` present year + 5 years
Consider the following example:
Example: The age of father 2 years ago 7 times the age of his son. At present, fathers age is five times that of his son . What are the ages of father and son at present?
Solution: Let present age of son = `x`
present age of father = `y`
Age 2 years ago

Present age


Son

`x`  2

`x`

Father

`7(x2)`

`y = 5x`

Start with the present age son
Then read the question and write the given equations.
Last step, Just make an equation using values of father's age.
Either, convert it both into present ages or 2 years ago
2years ago, `7(x2)` = `5x2`.............................................. 5x is present age of father. I converted it into age before 2 years
So equation is, `7(x2) = (5x2)`
Solving equation, x =`6` yrs
Therefore, present age of son = `6`yrs and
present age of father = `5 times 6` = `30` yrs
Example2: The age of father after 2 years is 4 times the age of his son. At present, father's age is five times that of his son . What are the ages of father and son at present?
Solution: The difference between both of examples is just ,one is 2 yrs ago and other is 2yrs hence.
Let present age of son = `x` yrs and
present age of father = `y` yrs
Present age

Age after 2 years
 
Son

`x`

`x+2`

Father

`y = 5x`

`4(x+2)`

Similarly, make an equation using values of father's age.
Either, convert it both into present ages or 2 years ago
2years hence, `4(x+ 2)` = `5x+2`.............................................. 5x is present age of father. I converted it into age after 2 years
So equation is, `4(x+2) = (5x+2)`
Solving equation, x =`6` yrs
Therefore, present age of son = `6`yrs and
present age of father = `5 times 6` = `30` yrs.
Example3: 2 yrs earlier father's age was 7 times the age of his son. 2 years hence father's age would be 4 times the age of his son. What are the present ages of father and son?
Solution: Let present age of son = `x` yrs and
present age of father = `y` yrs
Age 2 years ago

Present age

Age 2 years hence


Son

`x – 2`

`x`

`x+2`

Father

`7(x2)`

`y`

`4(x+2)`

Making an equation using values of father's age.
2years ago, `7(x2)` = `4(x+2) 4`
Here,4(x+2) is age after two years.Therefore, I converted it into age before 2 years by subtracted 4 years.
So equation is, `7(x2)` =`4(x+2)4`
Solving equation, x =`6` yrs
Therefore, present age of son = `6`yrs and
present age of father = `7(x2)` + 2 (i.e. age before 2 years + 2 = present age)
⇒ `7(4) + 2` = `28 +2` = `30`yrs.
Shortcut of these questions:
Age 2 years ago

Present age

Age 2 years hence


Father’s
age as compared to son

7

5

4

Shortcut of these three examples are very simple. Must try it once as it saves your time in exams. You should definitely try this once. But if you are not comfortable then you can do with the previous method.
Also check: Tricks of ratio and proportions
one more shortcut, which is applicable for all age problems.
ReplyDeleteEx 1:
Ratio of father : son
2 years ago 7 : 1 (here difference is 71=6)
Present 5 : 1 (here difference is 51=4)
to make same difference, multiply 4 with 7 : 1 and 6 with 5 : 1
Now their ages becomes,
2 years ago 28 : 4
Present 30 : 6
what if the difference is same
Deletein first example i think it need a correction please correct that one let us assume age of son is "x" 2 years ago at that time father's age is 7x,,,,,at present ages of son and father are x+2, 5(x+2),,,,,,,from that statement given we can equalize.........5(x+2)=5x we can solve and we get x=5 that means 2 years ago now 5+2=7years fathers age 5*7=35
ReplyDelete