ps question, pls help.

akkala wrote:If Dave works alone he will take 20 more hours to complete a task than if he worked with Diana to complete the task. If Diana works alone, she will take 5 more hours to complete the complete the task, then if she worked with Dave to complete the task? What is the ratio of the time taken by Dave to that taken by Diana if each of them worked alone to complete the task?

A. 4 : 1

B. 2 : 1

C. 10 : 1

D. 3 : 1

E. 1 : 2

Ans: B

Not sure how to solve this

I would go for B 2:1

let Dave and diana together take X hours

Dave can complete in x+20 hours

therefore diana can work in
1/X - 1/X+20 hrs which is 20/x(x+20) hrs-----------------------------1


Question stem says diana takes X + 5 hours
therefore in 1 day it will be 1/x+5 hours --------------------------------2

Equate 1 and 2

20/x(x+20) = 1/(x+5)

solve for X ,

x= 10 hours


thus dave takes 30 hours and diana takes 15 hours

hence the ratio is 30/15 = 2:1 hence B

Hope that helps... Plese let me know if you have any doubts

thx sudhir, that helps

sudhir3127 wrote: therefore diana can work in
1/X - 1/X+20 hrs which is 20/x(x+20) hrs-----------------------------1

rrrr, I am stuck with this...
1/X - 1/X+20 hrs which is 20/x(x+20) hrs

i don't know how you arived to it
help please

Yeh, clear i found my mistake