Time and work calculation

Can anyone help me to answer this question

A can do a piece of work in 7 days of 9 hours each and B can do it in 6 days of 7 hours each. How long will they take to do it working together 8 2/5 hours a day

Thanks Pramod

• Hi and welcome to the site! Since this is a site that encourages and helps with learning, it is best if you show your own ideas and efforts in solving the question. Can you edit your question to add your thoughts and ideas about it? – 5xum Feb 25 '15 at 11:28
• We can think of this problem as being analogous of analyzing a wave. Think of a piece of work as a single cycle, and the time to complete a single piece of work as the Period. – John Joy Feb 25 '15 at 15:21

For $A$ : $7$ days $\times 9=63$ hours to complete the work. For $B$ : $6$ days $\times 7=42$ hours to complete the work. So, in $1$ hour, $A$ makes $\frac{1}{63}$ of the work and $B$ makes $\frac{1}{42}$ of the work.
So, now, what is the work done by $A$ and $B$ together in $1$ hour and then how many hours are required for completing the work ? And now, you know that one day they work together corresponds to $8 \frac 25$ hours. So, how many days ?