SEARCH HOME
 Math Central Quandaries & Queries
 Question from Chamundeswari: How do I explain this problem to a year 3 kid? Fireman Fred needs to stay fit for his job. He runs 4.5km, 4 mornings, a week . if it takes him 4 minutes and 15 seconds on average to run 1km, how much time does he spend running over 4 weeks?

I have never taught at that level but here is a method you could try.

If he runs 4.5 km per morning then he runs $4.5 + 4.5 = 9$ km in 2 mornings. Thus for 4 mornings you have to double that to get 18 km every week.

If it took fireman Fred 4 minutes to run a kilometer then it would take him 4 times 18 = 72 minutes to run 18 kilometers. But it takes him 4 minutes and 15 seconds to run one kilometer so it will take him 18 more 15 second time interval to run the 18 kilometers. 4 times 15 seconds is a minute so it takes him 4.5 extra minutes. Thus to run 4.5 km, 4 times a week takes $72 + 4.5 = 76.5$ minutes.

If he does this for 2 weeks that takes $76.5 + 76.5 = 152 + 1 = 153$ minutes and hence for 4 weeks that's $153+153=306$ minutes.

I hope that helps,
Penny