Ssc ibps rrb tricks on problem on ages and boats & streams

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Problems on Ages, Trains, Boats and Streams Formulas and Tricks 


Problems on Ages Formulas - Formulas – 
 If the current age is x, then n times the age is nx.
 If the current age is x, then age n years later/hence = x + n.
 If the current age is x, then age n years ago = x – n.
 The ages in a ratio a : b will be ax and bx.
 If the current age is x, then 1/n times the age is x/n.


Quicker Methods –

 To find out son’s age, use this formula –

If t1 years earlier the father’s age was x times that of his son. At present the father’s age is y times that of his son. Then the present age of son will be?

Son’s Age = t1 (x-1) / (x-y)


 If present age of the father is y times the age of his son. After t2years the father’s age become z times the age of his son. Then the present age of son will be?

Son’s Age = (z-1)t1 / (y-z)


 t1 years earlier, the age of the father was x times the age of his son. After t2 years, the father’s age becomes x times the age of his son. Then the present age of son will be?

Son’s Age = [(z-1)t2  +  (x-1)t1] / (x-z)


 Son’s or Daughter’s Age = [Total ages + No. of years ago (Times – 1)] / (Times+1)


 Son’s or Daughter’s Age = [Total ages – No. of years ago (Times – 1)] / (Times+1)


 Father : Son

Present Age = x : y
T years before = a : b

Then, Son’s age = y * [ T(a-b) / Difference of cross product ]
And Father’s age = x * [ T(a-b) / Difference of cross product ]



Problem on Trains Formulas -


 When x and y trains are moving in opposite direction, then their relative speed = Speed of x + Speed of y


 When x and y trains are moving in same direction, then their relative speed = Speed of x – Speed of y


 When a train passes a platform, it should travel the length equal to the sum of the lengths of train & platform both.


 Distance = (Difference in Distance) * [(Sum of Speed) / (Diff in Speed)]


 Length of Train = [(Length of Platform) / (Difference in Time)] * (Time taken to cross a stationary pole or man)


 Speed of faster train = (Average length of two trains) * [(1/Opposite Direction’s Time) + (1/Same Direction’s Time)]


 Speed of slower train = (Average length of two trains) * [(1/Opposite Direction’s Time) – (1/Same Direction’s Time)]


 Length of the train = [(Difference in Speed of two men) * T1 * T2)] / (T2-T1)


 Length of the train = [(Difference in Speed) * T1 * T2)] / (T1-T2)


 Length of the train = [(Time to pass a pole) * (Length of the platform)] / (Diff in time to cross a pole and platform)


 First train’s starting point = S1 * [{(Total Distance) – S2 * (T1-T2)} / (S1+S2)]


 S2 = S1 * Square root of [(Time taken by first train after meeting) / (time taken by second train after meeting)]



Boats and Streams Formulas -


 If the speed of the boat is x and if the speed of the stream is y while upstream then the effective speed of the boat is = x – y


 And if downstream then the speed of the boat = x + y


 If x km/hr be the man’s rate in still water and y km/hr is the rate of the current. Then

Man’s rate with current = x + y
Man’s rate against current = x – y


 A man can row x km/hr in still water. If in a stream which is flowing at y km/hr, it takes him z hrs to row to a place and back, the distance between the two places is = z * (x2 – y2) / 2x


 A man rows a certain distance downstream in x hours and returns the same distance in y hours. If the stream flows at the rate of z km/hr, then the speed of the man in still water is given by – z* (x + y) / (y – x) km/hr.


 Man’s rate against current = Man’s rate with current – 2 * rate of current


 Distance = Total Time * [(Speed in still water)2 – (Speed of current)2] / 2 * (Speed in still water)


 Speed in Still Water = [(Rate of Stream) * (Sum of upstream and downstream time)] / (Diff of upstream and downstream time)

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