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Piyush covers a certain distance on bike. Had he moved 3 km/h faster, he would have taken 20 min less. If he had moved 2 km/h slower, he would have taken 20 min more. The distance covered (in km) is:

Solution

✅ Correct Option: 2

Piyush travels some distance on his bike. If he moves 3 km/h faster, he takes 20 minutes less. If he moves 2 km/h slower, he takes 20 minutes more.

Let Distance = DD km, Normal Speed = SS km/h, and Normal Time = TT hours.

Distance = Speed × Time, so D=STD = ST


Converting 20 minutes to hours: 20 minutes = 2060=13\frac{20}{60} = \frac{1}{3} hour


When speed is 3 km/h faster:

New speed = (S+3)(S + 3) km/h

New time = (T−13)(T - \frac{1}{3}) hours

Distance remains the same:

D=(S+3)(T−13)D = (S + 3)(T - \frac{1}{3})

Since D=STD = ST:

ST=(S+3)(T−13)ST = (S + 3)(T - \frac{1}{3})

ST=ST−S3+3T−1ST = ST - \frac{S}{3} + 3T - 1

0=−S3+3T−10 = -\frac{S}{3} + 3T - 1

S3=3T−1\frac{S}{3} = 3T - 1

S=9T−3S = 9T - 3 ... (Equation A)


When speed is 2 km/h slower:

New speed = (S−2)(S - 2) km/h

New time = (T+13)(T + \frac{1}{3}) hours

ST=(S−2)(T+13)ST = (S - 2)(T + \frac{1}{3})

ST=ST+S3−2T−23ST = ST + \frac{S}{3} - 2T - \frac{2}{3}

0=S3−2T−230 = \frac{S}{3} - 2T - \frac{2}{3}

S3=2T+23\frac{S}{3} = 2T + \frac{2}{3}

S=6T+2S = 6T + 2 ... (Equation B)


From Equations A and B:

9T−3=6T+29T - 3 = 6T + 2

3T=53T = 5

T=53T = \frac{5}{3} hours


Substituting T=53T = \frac{5}{3} into Equation B:

S=6(53)+2S = 6(\frac{5}{3}) + 2

S=10+2S = 10 + 2

S=12S = 12 km/h


Distance = Speed × Time:

D=12×53D = 12 \times \frac{5}{3}

D=603D = \frac{60}{3}

D=20D = 20 km

Therefore, the distance covered is 20 km.

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