Solve: It takes Danny 1 h to milk all of the cows, and it takes his sister 1.5 h. How long will it take to do the job together?
2007-03-26 09:06:25 · 6 answers · asked by soccerstar11 3 in Education & Reference ➔ Homework Help
Danny works at the rate of 1 "job" per hour. Danny's sister works at the rate of 1 job per 1.5 hours, or 1/1.5 jobs-per-hour. So after a certain fraction of an hour, say "t" hours, Danny does (1 job / 1 hour)*t of the job and his sister does (1 job / 1.5 hours)*t of the job. You want these fractions to equal one whole job together, so:
(1 job / 1 hr)*t + (1 job / 1.5 hr)*t = 1 job
t + (1/1.5)t = 1
t(1 + 1/1.5) = 1
t(1 + 10/15) = 1
t(15/15 + 10/15) = 1
t(25/15) = 1
t = 15/25 = 3/5
3/5 of an hour is the same as 36/60 of an hour, or 36 minutes.
2007-03-26 09:29:46 · answer #1 · answered by Anonymous · 0⤊ 0⤋
Danny works 1.5 times as fast as his sister.
Together they work 1 + 1.5 = 2.5 times as fast as the sister.
They therefore take 1.5/2.5 = 3/5hr = 3*60/5 = 36min.
2007-03-26 16:28:40 · answer #2 · answered by Anonymous · 0⤊ 0⤋
Tricky, aren't you? The 40 minutes is a good answer--giving them a moment or two to talk. You could say 37 1/2--but that's not practical.
2007-03-26 16:16:54 · answer #3 · answered by Anonymous · 0⤊ 1⤋
how many cows.... take 2.5 hours( i plus 1.5) and multiply by the ammount of cows. should work
2007-03-26 16:09:43 · answer #4 · answered by ♥愛♥ 2 · 0⤊ 0⤋
40 minutes???
2007-03-26 16:09:14 · answer #5 · answered by brandi 2 · 0⤊ 1⤋
let them both do it alone
2007-03-26 16:08:46 · answer #6 · answered by Mary 5 · 0⤊ 1⤋