Generate Random Numbers for two different column in c# with asp.net

I am developing one web application using platform c# and asp.net.

In my web form i have two different value which fetched from database.

Suppose value1=20 and value2=30.

Now the total of those values is 50.

My question is how can i generate random number for 50 and assign it to value1 and value2. But one condition should be fulfilled before displaying random number. values1 will start from 1 to 20 and value2 will start from 1 to 30 but random number should be assign to both value uniquely from 50.