Sainik School Entrance Exam 2020 Solved Paper

Question : 36 of 150

Marks: +1, -0

A car covers

300 {\kms}

at a constant speed. If its speed was

10 {\kmph}

more, it would have taken 1 hour less to travel the same distance. Find the speed of the car.

Solution:

(b) Distance

=300 {\km}

Suppose that, speed

=s {\km}

/ {h}

Then,

{300}/{s}-{300}/{s+10}=1

hour

⇒ 300[{1}/{s}-{1}/{s+10}]=1

⇒ 300[{s+10-s}/{s(s+10)}]=1

⇒ {10}/{s(s+10)}={1}/{300}

⇒ s(s+10)=3000

⇒ s^2+10 s-3000=0

⇒ s^2+60 s-50 s-3000=0

⇒ s(s+60)-50(s+60)=0

⇒ (s+60)(s-50)=0

either,

s+60=0

s-50=0

∴

s=-60

s=50

..............................[

-60

is ignoring]
The speed of the car

=50 {\km}

/ {\r}

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