A bike can finish a certain journey in 6 hours at the speed of 92 km/hr. In order to cover the same distance in 3 hours, the speed of the bike (in km/hr) must be increased by ____.
- AOption (a)
92
- BOption (b)
85
- COption (c)
86
- DOption (d)
98
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Correct answer
92
Why this answer is correct
Shortcut Trick
Time ratio (Initial : New) = 6 : 3 = 2 : 1
Since Distance is constant, Speed ratio is inverse of Time ratio = 1 : 2
1 unit (Initial Speed) = 92 km/hr
Increase in speed required = 2 − 1 = 1 unit = 92 km/hr
∴ The correct answer is 92 km/hr.
Alternate Method
Given: Initial Speed = 92 km/hr, Initial Time = 6 hours, New Time = 3 hours
Formula Used: Distance = Speed × Time
⇒ Total Distance = 92 km/hr × 6 hours
⇒ Total Distance = 552 km
⇒ Required New Speed = Total Distance ÷ New Time
⇒ New Speed = 552 ÷ 3 = 184 km/hr
⇒ Increase in Speed = New Speed − Initial Speed
⇒ Increase in Speed = 184 − 92 = 92 km/hr
∴ The correct answer is 92 km/hr.
Additional Information
Inverse Variation Rule
When distance is constant, speed and time are inversely proportional (S1 × T1 = S2 × T2).
Average Speed
If a journey is covered in two equal distances at speeds x and y, average speed = 2xy ÷ (x + y).
Relative Speed
Speed of two objects moving in the same direction is (S1 − S2) and in opposite directions is (S1 + S2).