Multiple choice

The distance covered by a train in (5y-1) hours is (125y3-1)km. The speed of the train is:

  1. (5y3-1) km/h

  2. (25y2-5y+1) km/h

  3. (5y+1) km/h

  4. (25y2+5y+1) km/h
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Speed = Distance/Time = (125y³-1)/(5y-1). Using a³-b³ = (a-b)(a²+ab+b²), we get 125y³-1 = (5y)³-1³ = (5y-1)(25y²+5y+1). Therefore Speed = (25y²+5y+1) km/h. Option D is correct.

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