math
posted by cliff .
john types 20 pages in 40 min, sue types 20 pages in 30 min, bob types 20 pages in 24 min. working togehter how long to type 20 paqes

john types 20/40 or 1/2 page/min
Sue types 20/30 or 2/3 page/min
Bob types 20/24 or 5/6 page/min
combined rate = 1/2 + 2/3 + 5/6 or 2 pages per minute
time at combined rate = 20/2 or 10 minutes