Please help with this MATHS PROBLEM!!!?
an express train starts from chennai at a speed of 50 km/hr. after one hour an another express starts at a speed of 70 km/hr. after how many hours will the second express train cross the first?
please reply me with the correct answer with steps.
THE OPTIONS ARE:
a) 3 hours b) 2 3/4 hrs c) 3 1/2 hrs d) 2 1/4 hrs e) none of these
2007-01-07 19:30:48 · 11 answers · asked by krithika R 1 in Education & Reference ➔ Homework Help
Let 'X' be the time travelled by first train before it is overtaken
then distance travelled by the first train will be 50X
Second train starts 1 hour later hence the second train travels for (X-1) hours
Hence distance traveled by second train is 70(X-1)
the train is overtaking so
50 X = 70(X-1)
50X= 70X-70
20X= 70
Hence X= 3.5
Ans is 3.5 hours.
hope u r satisfied.
god bless.
2007-01-07 19:51:06 · answer #1 · answered by sweet tooth 2 · 1⤊ 0⤋
Answer is 3 1/2 hours.
see distance= speed *time.the point where the second train over takes the first is when both of them would have travelled equal distance. let the time for which the first train travelled before being overtaken be x hours then second train travels for x-1 hours. In that case equate the distances covered by each train as
50* x=70*(x-1)
solve this to get x=3 1/2
hence first train travels for 3 1/2 hours while the second one for 2 1/2 hours
2007-01-08 05:16:44 · answer #2 · answered by Anonymous · 0⤊ 0⤋
Let the train with a speed of 50km/hr be called train A and
train with a speed of 70km/hr be called train B
As train B starts one hour later ; therefore,
Distance travelled by train A in 1 hour =50*1 km (d = s*t)
=50 km
relative velocity of train B w.r.t. train A =(70 - 50) km/hr
= 20 km/hr
time taken by train B to cross train A = 50/20 hrs
= 2.5hrs after the train B has started
therefore,the total time taken by train B=(2.5+1)hrs.
=3.5hrs. from start of train A
which is equivalent to 3 1/2 hrs
Hence, option c) is correct
2007-01-08 03:45:55 · answer #3 · answered by niti 2 · 0⤊ 0⤋
The answer is 2 hours 15 mins.
If train A left at midday at a speed of 50 kph then in 2 hours it would have done 100 kms.
If train B left at 1:00 pm (1 hour later) then at 2:00pm it would have done only 70 kms.
If train A did 50 kph then in 3 hours it would have done 150 kms.
And if it left at midday then at 3:00pm it would have done 150 kms.
So if train B left at 1:00 pm at 70 kph. then by 3:00 pm it would have travelled 140 kms (10 kms to catch at this time).
And i think your smart enough to work that remainder out..
Remember... you dont get stupid questions.
Thanks for asking :)
2007-01-07 19:59:23 · answer #4 · answered by jstr12001 3 · 0⤊ 0⤋
After "X" hours, the first train travels a distance D1 = 50 + 50X
After "X" hours, the second train travels a distance D2 = 70X
For the second train to cross the first we must have D1 = D2
or 50 + 50X = 70X => 50 = 70X - 50X => X =21/2 hrs
The correct answer is "e"
P.S: "X" is the travel time of the second train.
2007-01-08 05:01:23 · answer #5 · answered by lloyd w 1 · 0⤊ 0⤋
After 1 hour 1st train is 50 km from start, 2nd one starts.
After 2 hrs 1st train is 100km from start, 2nd one is 70 km from start.
After 3 hrs 1st train is 150km from start, 2nd one is 140km from start.
After 3hrs 30 mins 1st train is 175km from start, 2nd one is 175 km from start.
It will therefore take 3 hrs 30 mins from When the 1st train starts, and 2 hrs 30 mins from when 2nd train starts until they meet.
2007-01-07 19:38:41 · answer #6 · answered by Anonymous · 1⤊ 0⤋
2 n 2 only.
2007-01-08 01:34:47 · answer #7 · answered by Anonymous · 0⤊ 0⤋
21/2 hr
2007-01-07 20:14:47 · answer #8 · answered by david j 5 · 0⤊ 0⤋
what was the destination between the 2 trains before they start ?? ???
2007-01-07 19:34:17 · answer #9 · answered by Reasonable 3 · 0⤊ 0⤋
The answer is E.
Check the last question you posted, I answered in there and explained how I got the answer.
2007-01-07 19:32:56 · answer #10 · answered by Phoenix 3 · 0⤊ 1⤋