Two pipes P and Q can fill a cistern in 15 and 20 minutes respectively. Both pipes are opened together, after how many minutes should Q be turned off, so that the cistern be fill in 12 minutes?
A
9 minutes
B
6 minutes
C
4 minutes
D
8 minutes
উত্তরের বিবরণ
Question: Two pipes P and Q can fill a cistern in 15 and 20 minutes respectively. Both pipes are opened together, after how many minutes should Q be turned off, so that the cistern be fill in 12 minutes?
Solution:
P can fill the cistern in 15 minutes
So in 1 min P can fill the cistern = 1/15 th part
In 12 min, P can fill the cistern = 12/15
= 4/5 part
Remaining part = 1- (4/5) part
= 1/5 part
As Q can fill full cistern in 20 minutes
So it will fill 1/5 part in = (1/5) × 20 = 4 minutes.
∴ Pipe Q should be turned off after 4 minutes.
0
Updated: 2 weeks ago
A man rows downstream at 32 km/h and rows upstream at 22 km/h. At what speed can he row in still water?
Created: 2 weeks ago
A
27 km/h
B
5 km/h
C
54 km/h
D
15 km/h
Question: A man rows downstream at 32 km/h and rows upstream at 22 km/h. At what speed can he row in still water?
Solution:
Given,
Man rows downstream = 32 km/h
Man rows upstream = 22 km/h
We know that,
Speed in still water = (Downstream speed + Upstream speed) ÷ 2
= (32 + 22) ÷ 2
= 54 ÷ 2
= 27 km/h
0
Updated: 2 weeks ago
A motorboat, whose speed in 18 km/h in still water goes 36 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream is-
Created: 2 weeks ago
A
8 km/h
B
5 km/h
C
5.5 km/h
D
6 km/h
Question: A motorboat, whose speed in 18 km/h in still water goes 36 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream is-
Solution:
Let, the speed of the stream = x km/h
Then,
Speed downstream = (18 + x) km/h
Speed upstream = (18 - x) km/h
ATQ,
36/(18 + x) + 36/(18 - x) = 4.5
⇒ 36{(18 + x) + (18 - x)}/(18 + x)(18 - x) = 4.5
⇒ 1296/(324 - x2) = 9/2
⇒ 9(324 - x2) = 2 × 1296
⇒ 2916 - 2592 = 9x2
⇒ 9x2 = 324
⇒ x2 = 36 = 62
∴ x = 6
∴ The speed of the stream is 6 km/h
0
Updated: 2 weeks ago
Working 5 hours a day, A can complete a work in 9 days and working 9 hours a day, B can complete the same work in 10 days. Working 6 hours a day, they can jointly complete the work in-
Created: 2 weeks ago
A
5 days
B
7 days
C
8 days
D
6 days
Question: Working 5 hours a day, A can complete a work in 9 days and working 9 hours a day, B can complete the same work in 10 days. Working 6 hours a day, they can jointly complete the work in -
Solution:
Working 5 hours a day, for 9 days, A can finish the work in = (5 × 9) = 45 hours
Working 9 hours a day, for 10 days, B can finish the work in = (9 × 10) = 90 hours
both together can do in one hour = 1/45 + 1/90
= (2 + 1)/90
= 3/90
= 1/30
so, it will take them 30 hours to do the work.
hence, working 6 hours a day, they need = 30/6 = 5 days
So they will complete the work in 5 days working 6 hours each day.
0
Updated: 2 weeks ago
