Question

Melissa and Rory live near a bike trail, 21 km apart. They plan to meet at a park mid-way between their homes. They start from their homes at the same moment, and ride toward each other. Both ride at 7 km/hour. Melissa’s dog Jessie knows this routine. He starts with Melissa, and runs at 18 km/hour toward Rory. When he reaches Rory, he turns around and runs toward Melissa. He reaches Melissa, turns around and runs toward Rory again, and so on, until Melissa and Rory meet. How many kilometers did Jessie run?

Answer 1

27km.

Step-by-step explanation:

Jessie will run for a duration of time, which is the time it takes for Melissa and Rory to meet each other.

Together combined, Melissa and Rory runs at 14km/h. The bike trail is 21km, so it will take 1.5 hours.

Jessie runs at 18km/h, so Jessie will run 18 * 1.5 = 27km.