Say Frank can build a model airplane in 3 days, Jo can do it in 2, but Moe can only do it in 5 days. If they work together, they’ll build a model plane in:
Possible Answers
Selected Possible Answer

0.5 days

0.76 days

10 days

0.97 days

2 days

Question

Say Frank can build a model airplane in 3 days, Jo can do it in 2, but Moe can only do it in 5 days. If they work together, they’ll build a model plane in:
Possible Answers
    Selected 	Possible Answer
    	

    0.5 days
    	

    0.76 days
    	

    10 days
    	

    0.97 days
    	

    2 days

anonymous · Answer

i think its 0.76 im not sure really i think its the rule of 3

anonymous · Answer

a/b = c/x

anonymous · Answer

nope its not 0.76 thats what i guessed.

anonymous · Answer

would it be 2 days?
since that is the fastest jo can do it

anonymous · Answer

thats the best i can think of sorry

anonymous · Answer

$$T_{F} = 3, T_{Jo} = 2, T_{Moe} = 5$$$$R_{F} = W/T_{F}, R_{Jo} = W/T_{Jo}, R_{M} = W/T_{M}$$
W is work to be done to build a model airplane, R rate of work of wach person
when three work together time taken $$W/(W/T_{F} +W/T_{Jo} +W/T_{M})$$
0.97 days

anonymous · Answer

@sumanth4phy what formula is that? Rate = work / time? could you explain what you did there?

anonymous · Answer

I see how you add their separate rates but why what are you dividing?

anonymous · Answer

yeah Rate/Speed at which work is done = W/T
I need time so T=W/R hence the division

anonymous · Answer

OH gotcha riiight