Speed and time change by fixed amounts over a fixed distance: quadratic for speed, time or distance

This type of question, asked 5 times: CDS 1 2020, CDS 2 2020, CDS 1 2022, CDS 2 2022, CDS 2 2026. All 7 questions below, oldest first.

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Question 1
CDS 1 2020
29 $A train takes two hours less for a journey of 300 km if its speed is increased by 5 km/hr from its usual speed. What is its usual speed ?$
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Question 2
CDS 2 2020
24 $By increasing the speed of his car by 15 km/hr, a person covers a distance of 300 km by taking an hour less than before. What was the original speed of the car ?$
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Question 3
CDS 2 2020
41 $A car did a journey in t hours. Had the average speed been x kmph greater, the journey would have taken y hours less. How long was the journey ?$
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Question 4
CDS 1 2022
40 $X$
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Question 5
CDS 1 2022
28 $p$
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Question 6
CDS 2 2022
34 $In a flight of 2800 km, an aircraft was slowed down due to bad weather. Its average speed for the trip was reduced by 100 km/hr and time of flight increased by 30 minutes. What was the original average speed of the aircraft ?$
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Question 7
CDS 2 2026
14 $Had I walked 0.5 km/hr faster, I would have taken 8 minutes less to walk 2 km. What is my original speed ?$
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Question 1