[user1285]

Originally Posted by poojadatta

Two Person A and B started walking simultaneously from two point P and Q respectively along PS and QR the length of rectangle PQRS. By the time A reach S, B has reached T,the mid-point of QR. At this point they exchange their speed and continue walking towards R. If the length of the rectangle is 3 time its breath what should be the ration of present speed of A and B, so they reach R simultaneously.

1) 1:1 2) 2:3 3) 1:2 4) 4:5 5)3:2

Have a basic doubt
A walks alon PS
B along QR
Both PS and QR have same lengh
When A reaches S , B reaches half the length of QR -
Speed of A : Speed of B =2:1
After exchanging it it will be 1: 2
where am i going wrong ??

[raghav507]

Originally Posted by poojadatta

49/27

S = 1+4/7+(9/7^2)+(16/7^3)+(25/7^4)+......(1)
multiply (1) with 7
7S = 7+4+(9/7)+(16/7^2)+(25/7^3)+......(2)
(2)-(1)
6S = 10+(5/7)+(7/7^2)+(9/7^3)+......(3)
multiply (3) with 7 again
7*6S = 70+5+(7/7)+(9/7^2)+(11/7^3)......(4)
(4)-(3)
36S = 65 + 2(1/7 + 1/7^2 + .......)
= 65 + 2*1/6 = 196/3
=> S = 49/27

Ok this might be a silly question but I did not get the bold part.. can some help

my comments in bold...
hope it helps...

[masoom]

Originally Posted by poojadatta

49/27

S = 1+4/7+(9/7^2)+(16/7^3)+(25/7^4)+......
7S = 7+4+(9/7)+(16/7^2)+(25/7^3)+......
6S = 10+(5/7)+(7/7^2)+(9/7^3)+......

7*6S = 70+5+(7/7)+(9/7^2)+(11/7^3)......
36S = 65 + 2(1/7 + 1/7^2 + .......)
= 65 + 2*1/6 = 196/3
=> S = 49/27

Ok this might be a silly question but I did not get the bold part.. can some help[/quote]

@pooja no question is silly to ask..

i tell you a standard method to tackle these type of problems..

whenever there is a series...

which gives a hint of GP and AP .. we always do sum by

multiplying by the common ratio...

here by observation we can find that CR is 1/7..

and the double difference of numerators are in AP...

so s=1+4/7+9/7^2+16/7^3...

1/7s= 1/7 + 4/7^2 + 9/7^3..

on subtracting : 6/7s= 1+ 3/7+5/7^2+..

now numerators are in AP.... so again repeat the same operation..

6/49s= 1/7+ 3/7^2+...

so 6/7s-6/49s= 1+ 2/7+2/7^2+....

i think u can proceed from here..

[hi.shivani]

Originally Posted by masoom

what i think is that...

there is no need of the info that they exchange their speed..

as we have to find ratio of their current spped..

let length=l so breadth = l/3..

now let the correspinding speeds are v1, and v2..

so one person has to cover bredath ie l/3..

and other has to cover half the length ie l/2..

so (l/3)/(1/2)=v1/v2..

so from here v1/v2=2/3..

But how can we assume that PQ and QS is the length only??
If it is breadth then the ratio turnout to be 6:1.

[poojadatta]

Originally Posted by hi.shivani

But how can we assume that PQ and QS is the length only??
If it is breadth then the ratio turnout to be 6:1.

In question its given
PS and QR the length of rectangle PQRS

[poojadatta]

What I did was this
PS and QR are length and PQ ans SR are breath....
Time taken by A to travel PS

t1=3/s1-----1

In the same time B traveled QT which is

1.5=s2*(3/s1)----2

on solving 2 we get s2/s1=1/2

Now if we exchange the speed (it is exchange in ques then ino need to solve ans is 2:1 will become answer but if its change then which it should be as there is further question asked)
Now time take to travel by B from TQ is same as A takes to travel SR...

tB=1.5/y and tA=1/z (where y and z are speed of A and B after changing)

now tA=tB

1.5/y=1/z

z/y=2:3

So they have printing mistake it should be change..... as answer is 2:3

[KillFRenzy]

Originally Posted by masoom

what i think is that...

there is no need of the info that they exchange their speed..

as we have to find ratio of their current spped..

let length=l so breadth = l/3..

now let the correspinding speeds are v1, and v2..

so one person has to cover bredth ie l/3..

and other has to cover half the length ie l/2..

so (l/3)/(1/2)=v1/v2..

so from here v1/v2=2/3..

and other has to cover half the length ie l/2..
other will cover half the breath...not half the length...hence l/6
v1/v2 = 2/1...

Now Remaining distance is...
for A (in order to reach R..it needs to cover entire length)
hence L.
for B, another L/6(coz breath is L/3..(and it already covered L/6))

hence speed ratio = 6:1

[dare2]

lets do one more question on series.

find the sum of the first 50 terms of the series:
3, 7, 19, 45, 91, ............

[poojadatta]

Originally Posted by KillFRenzy

and other has to cover half the length ie l/2..
other will cover half the breath...not half the length...hence l/6
v1/v2 = 2/1...

Now Remaining distance is...
for A (in order to reach R..it needs to cover entire length)
hence L.
for B, another L/6(coz breath is L/3..(and it already covered L/6))

hence speed ratio = 6:1

Its given that they travel on length PS and QR.. check out my solution hope its useful

[poojadatta]

Each of two lifting machine delivering only 90% of its rated power, works for 6 hours per day for 4 days and lifts 4500 tonnes of material. If three such machines, delivering only 80% of the same rated power as first two machines, are scheduled to lift 6000 tonnes in 3 days, how may hours per day should each vehicle works

1)4 2) 2 3) 6 4) 8 5) 18

Any take for this I am confused with directly proportional and indirect proportional....