1. Rate question

If 9 cows can eat 4 bales of hay in 5 days, how long will it take 4 cows to eat 17 bales of hay?

I do not remember how to do this at all

2. Originally Posted by shinimai
If 9 cows can eat 4 bales of hay in 5 days, how long will it take 4 cows to eat 17 bales of hay?

I do not remember how to do this at all
4 bales eaten by 9 cows in 5 days

1 bale eaten by 9 cows in 5/4 days

1 bale eaten by 1 cow in 5*9/4 days

17 bales eaten by 1 cow in 17*5*9/4 days

17 bales eaten by 4 cows in 17*5*9/(4*4) days

3. Originally Posted by shinimai
If 9 cows can eat 4 bales of hay in 5 days, how long will it take 4 cows to eat 17 bales of hay?

I do not remember how to do this at all
This is where the unit analysis will help [and I'm doing it 'upside down from what Subhotosh Khan did, but the answer should be the same]. So the Rate R of using hay is
R = 4 bales per (9*5 cow-day) = 4 bales / (9*5 cow-day)
or
R = (4/45) bales /cow-day
Thus, at the same rate we want
R = (4/45) bales /cow-day = 17 bales / (4 * x cow-day)
or
x = 17 / 4 / (4/45) = 17 * 45 / 16

4. Is that how you approach all math problems? "Remembering" how to do them? What ever became of thinking?