I just have some niggling doubts on solving these problems. I'm aware of the method of 'picking numbers', but I seek a more general understanding. Could someone explain to me how to solve these problems generally? Or how to think of them.
1.) Bill has to type a paper that is pages long, with each page containing words. If Bill types an average of words per minute, how many hours will it take him to finish the paper?
2.) If David paints at the rate of houses per day, how many houses does he paint in days, in terms of and ?
It's . Try picking numbers for h and d. h = 4; d = 5. He paints 4 houses a day and he paints for 5 days he can paint 20 houses.
Multiplying the rate (h) by the number of days (d). Plugging in the respective values for and , only one gives 20. This is just following the 'pick numbers' method. The book also gives this answer.