Multiple choice

By increasing the speed of his car by 15 km/hr, a person covers a distance of 300 km by taking an hour less than before. What was the original speed of the car?

  1. 45 km/hr

  2. 50 km/hr

  3. 60 km/hr

  4. 75 km/hr
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let original speed be v. Time taken = 300/v. New time = 300/(v+15). We have 300/v - 300/(v+15) = 1. Solving v^2 + 15v - 4500 = 0 gives (v+75)(v-60)=0. Since speed is positive, v=60.

AI explanation

Using the formula time equals distance divided by speed, the difference between the original time and the new time is exactly one hour. Setting up the equation with the original speed as x, we get 300 divided by x minus 300 divided by (x plus 15) equals 1. Factoring the resulting quadratic equation, x squared plus 15x minus 4500 equals 0, gives (x minus 60) multiplied by (x plus 75) equals 0, meaning the original speed is 60 km/hr.

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