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IBPS RRB Office Assistant 13 Nov 2016 Paper
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© examsnet.com
Question : 67
Total: 80
A boat, whose speed is 15 km/ hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. What is the speed of the stream? (in km/hr)
10
6
5
4
15
Validate
Solution:
(3) Let the speed of current bex kmph.
∴ Rate downstream
= (x + 15) kmph.
Rate upstream = (15 – x) kmph.
According to the question,
30
x
+
15
+
30
15
−
x
=
4
1
2
⇒
30
(
15
−
x
+
15
+
x
(
15
+
x
)
(
15
−
x
)
)
=
9
2
⇒
900
225
−
x
2
=
9
2
⇒
100
225
−
x
2
=
1
2
⇒
225
−
x
2
=
200
⇒
x
2
=
225
−
200
=
25
⇒
x
=
√
25
=
5
k
m
p
h
© examsnet.com
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