I intitially wrote that you'd need to do it in 2 steps however you can do it in 1.
create a new query on the start dataset, select the columns you want summed and in the summary column change "None" to "SUM".
Then click on the computed columns button > New > Build Expression...
When it asks about calculated columns, say yes.
double click on the first summed column, then input a '/' after it, then double click on the second summed column.
Job done.
Chris
Business Analyst, Code Monkey, Data Wrangler.
SAS Guru.