Multiple choice

Jaspreet is going from New Delhi to Amritsar by Car. If he goes at a speed of 40 km./hr. and returns with a speed of (x) km./hr then find the value of (x) if the average speed of the whole journey is 80 km./hr.

  1. $160 km./hr$
  2. $40 km./hr$
  3. $120 km./hr$

  4. Can't be determined
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For equal distances, average speed = 2ab/(a+b), not arithmetic mean. With speeds 40 and x: 2(40)(x)/(40+x) = 80. Solving: 80x/(40+x) = 80, so 80x = 3200 + 80x, giving 0 = 3200, which is impossible. The equation has no solution - an 80 km/hr average is mathematically unattainable when one speed is 40 km/hr.

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