help

It would take 60 minutes for Mr. F. to eat 3 pounds of cereal, and it would take 90 minutes for Mr. T. To eat 3 pounds of cereal, so if they were eating together it would take 90 minutes for them to finish.

F rate    1 lb / 20 min

T rate    1 lb /30 min

3 / (1/20 + 1/30) = 36 minutes     

thank u so much  the solution was not what i thought of at all !!1

Always easy to solve this type of problem

1/20 + 1/30  =     [ 30 + 20 ] / 600  =  50/ 600  =  1 / 12

Take the reciprocal of the answer  ⇒   12 min   together  for 1 lb

So....36 min for 3 lb