solve it ...
it's from ncert maths book...
class 10...
Answers
Step-by-step explanation:
(i)-Let, speed of Ritu in still water be x km/hr
and speed of current be y km/hr
Then speed downstream =(x+y) km/hr
speed upstream =(x−y) km/hr
we know, Time=
Speed
Distance
Then
x+y
20
=2 and
x−y
4
=2
⇒x+y=10 ...(1)
& x−y=2 ...(2)
adding both we get, 2x=12⇒x=6
Thus using (1) y=10−6=4
Hence the speed of Ritu in still water is 6 km/hr and the speed of the current is 4 km/hr.
(ii)answr
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MATHS
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Asked on January 17, 2020 by
Yashi Azmi
2 women and 5 men can together finish an embroidery work in 4 days, while 3 women and 6 men can finish it in 3 days. Find the time taken by 1 woman as well as 1 man to finish the work if each of them works alone.
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ANSWER
Let the work done by man and woman per day be x and y respectively.
When the work is completed in 4 days
Since 5 men and 2 women complete the work in 4 days
therefore work done by 5 men and 2 women in 1 day =
4
1
∴5x+2y=
4
1
⟶eq
n
1
When the work is completed in 3 days
Since 6 men and 3 women complete the work in 3 days
therefore work done by 6 men and 3 women in 1 day =
3
1
∴6x+3y=
3
1
⟶eq
n
2
Multiplying by 3 in eq
n
1, we get
⇒15x+6y=
4
3
⟶eq
n
3
Multiplying by 2 in eq
n
2, we get
⇒12x+6y=
3
2
⟶eq
n
4
On subtracting eq
n
4 from eq
n
3, we get
⇒15x+6y−12x−6y=
4
3
−
3
2
⇒3x=
12
1
⇒x=
36
1
On substituting the value of x in eq
n
2, we get
⇒6×
36
1
+3y=
3
1
⇒3y=
3
1
−
6
1
⇒y=
18
1
Thus,
work done by 1 man in 1 day =
36
1
days
∴ Time taken by 1 man alone to finish the work =36 days
work done by 1 woman in 1 day =
18
1
days
∴ Time taken by 1 woman alone to finish the work =18 days
(iii)
MATHS
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Asked on December 27, 2019 by
Puneetha Spoorthi
Roohi travels 300 km to her home partly by train and partly by bus. She takes 4 hours if she travels 60 km by train and the remaining by bus. If she travels 100 km by train and the remaining by bus, she takes 10 minutes longer. Find the speed of the train and the bus separately.
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ANSWER
Let the speed of the train be x km/hr and the speed of the bus is y km/hr.
So according to question and using Time=
Speed
Distance
Total distance =300 km
Roohi travels 60 km by train and 300−60=240 by bus in 4 minute,
x
60
+
y
240
=4
and 100 km by train, 300−100=200 by bus, and takes 10 minutes more,
x
100
+
y
200
=4+
60
10
⇒
x
100
+
y
200
=
6
25
Now, let
x
1
=u and
y
1
=v
then 60u+240v=4.............eq1
100u+200v=
6
25
..............eq2
multiply eq1 by 5 and eq2 by 6 we get
300u+1200v=20..........eq3
600u+1200v=25...........eq4
Subtracting eq3 qnd eq4 we get
−300u=−5
u=
300
5
=
60
1
Putting the value of u in eq1 we get
60×
60
1
+240v=4
240v=3
v=
240
3
=
80
1
Now
x
1
=u=
60
1
∴x=60
and
y
1
=v=
80
1
∴y=80
Hence the speed of the train is 60 km/hr and the speed of the bus is 80 km/hr
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