Multiple choice

An aeroplane started $30$ minutes later than the schedule time from a place $1500km$ away from its destination to reach the destination at the schedule time the pilot had to increase the speed by $250$km/hr what was the speed of the aeroplane per hour during the journey?

  1. $100$km/hr
  2. $1000$km/hr
  3. $1050$km/hr
  4. $900$km/hr
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let v be the original speed. The time taken is 1500/v. With increased speed, time is 1500/(v+250). The difference is 0.5 hours. Solving 1500/v - 1500/(v+250) = 0.5 leads to v^2 + 250v - 750000 = 0. Factoring gives (v+1000)(v-750) = 0, so v = 750. The new speed is 750 + 250 = 1000 km/hr.

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