9. An aeroplane is flying at a speed of 900 km/h. What is the distance covered by it in 2 hours 15 minutes? b. What is the time taken to cover 150 km?
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Answer:
Given,
Distance = 400 km
Average speed of the aeroplane = x km/hr
And, speed while returning = (x+40) km/hr
We know that,
Time = Distance / Speed
(i) Time taken for onward journey = 400/x hrs
(ii) Time taken for return journey = 400/(x+40) hrs
Then, according to the question
x
400
−
x+40
400
=
60
30
x(x+40)
400x+16000−400x
=
2
1
x(x+40)
16000
=
2
1
x
2
+40x−32000=0
x
2
+200x−160x−32000=0
x(x+200)−160(x+200)=0
(x+200)(x−160)=0
So, x=−200 or 160
As the speed cannot be negative, x = 160 is only valid.
Step-by-step explanation:
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