Grades 7-8 Video Solutions 2025-2025_7-8

Video Transcription

Problem number 23. Underdog leaves for school at 8am. His school is 1km away. When he walks,  his speed is 4km per hour. When he bikes, his speed is 15km per hour. He is 5 minutes early  when he walks. How many minutes early is he when he bikes? Let's figure out how long it takes for  Underdog to reach school when he is walking and when he is biking. Since he walks at a speed of  4km per hour, to walk 1km, it will take 1 fourth of an hour, or 15 minutes. By the same logic,  when he bikes his speed is 15km per hour, so to bike for 1km, it will take 1 fifteenth of an hour,  which is 4 minutes. This means that biking takes 11 minutes less than walking. And so using this,  since he is 5 minutes early when he walks, he will be 5 plus 11, or 16 minutes early when he bikes. So that means that the answer is E, 16.

Video Summary

Underdog's school is 1km away. Walking at 4km/h, it takes him 15 minutes to walk, making him 5 minutes early. Biking at 15km/h, he takes 4 minutes, which is 11 minutes faster than walking. Therefore, when biking, he is 16 minutes early (5 minutes early when walking plus the 11 minutes saved by biking).