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UPSC 2016 CDS I Math Paper
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© examsnet.com
Question : 39
Total: 100
A passenger train takes 1 hour less for a journey of 120 km, if its speed is increased by 10 km/hour from its usual speed. What is its usual speed?
[2016 CDS-I]
50 km/hour
40 km/hour
35 km/hour
30 km/hour
Validate
Solution:
Let the usual speed of the train be x km/hour.
Time taken by the train at usual speed – Time taken by the train at increased speed = 1 hour
∴
120
x
−
120
x
+
10
=
1
⇒
1200
x
(
x
+
10
)
=
1
⇒
x
2
+
10
x
−
1200
=
0
⇒
(
x
+
40
)
(
x
−
30
)
=
0
⇒
x
=
30
(Speed of the train cannot be negative)
Thus, the usual speed of the train is 30 km/hour.
© examsnet.com
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