Question 1140365
A company has two large computers. The slower computer can send all the companies emails in 30 mins. The faster computer can complete the same job in 10 minutes. If both computers are working together, how long will it take to do the job? 
one can send all mail in 30 minutes 
it will take for 1 mail=1/30 minutes 
other will take  send all mail=10 minutes
this will take in 1 mail =1/10 minutes 
both will take for for 1  mail=1/10+1/30=4/30 minutes 
both working together it will take total time =30/4=7.5 minutes