Published: 05 Aug 2019

**1. Basics**

Speed = Distance / Time

Time = Distance / Speed

Distance = (Speed × Time)

**2. Convert kilometres per hour(km/hr) to metres per second(m/s)**

x km/hr = x * 5/18 m/sec

**3. Convert metres per second(m/s) to kilometres per hour(km/hr)**

x m/sec = x * 18/5 km/ hr

**4. Average Speed**

If an object covers a certain distance at xx kmph and an equal distance at yy kmph, the average speed of the whole journey

(2xy / x+y) kmph.

**5. Relation Between Distance, Speed and Time**

1. If the ratio of the speeds of A and B is a : b, then the ratio of the times taken by them to cover the same distance is

1/a : 1/b or b : a.

2. Speed and time are inversely proportional (when distance is constant)

Speed ∝ 1/time

3. Assume two objects A and B start at the same time in opposite directions from P and Q respectively. After passing each other, A reaches Q in aa seconds and B reaches P in bbseconds. Then,

Speed of A : Speed of B = root of b : root of a

4. An object covered a certain distance at a speed of vv kmph. If it had moved v_{1} kmph faster, it would have taken t_{1} hours less. If it had moved v_{2} kmph slower, it would have taken t_{2} hours more. Then,

v = v_{1}v_{2}(t_{1 }+ t_{2})/v_{1}t_{2} - v_{2}t_{1 }kmph

x = vt_{1} (1 + v/v_{1}) km

Special Case:

If t1=t2, v= 2v_{1}v_{2}/v_{1} - v_{2 }kmph

https://gyangossip.com/quantitative-aptitude/mock-test/T4531

https://gyangossip.com/quantitative-aptitude/mock-test/T9118