To get value of calculated field in another cell

Hi,

My sample report is

                          LessThan5yrs  6-10yr       11-20yr         20+yr           total

#ofCustomers     val1                 val2            val3             val4             val1+val2+val3+val4

% of customers   val1/( val1+val2+val3+val4)*100

Product1                val5            val6             val7          val8...

product2

.

.

Total

In the report getting values for val1 to val8.. from dataset.Now i am using different dataset for every value. I need to use close to 50 datset in report.I am wondering  is there any other way to reduce the number of dataset? for every value i need to run different query.

And then how can i use total(val1+val2+val3+val4) value to calculate %of customers? can i use variable?How to use variables? or any other way to reuse the calculated field?

Thank You