DB Design :: Summing From Two Tables Then Performing Operation With 2 Sums

I am using sql server and I have a table called accnt with the fields ven1 and amnt1 and a table called acc1167 with fields ven, job#, and amnt. for this example these tables look like this

       accnt                          acc1167
    ven1     amnt1              ven     job#   amnt
    1167     100                1167     1      200     
    1152     50                  1167     2      300
    1167     110                1167     3      100
    1167     300                1167     4      200
    1252     1050              1167     5      200
    1167     210                1167     6      150
    1167     1150 
    1167     130 
    2113     800 
    1167     550
    1167     1200

I need to sum amnt1 for all the records in accnt with the ven1 of 1167, we will call this sumA. Then sum amnt in acc1167 for all records, we will call this sumB. next I need to divide sumB by sumA to get a ratio. finally I need to multiply each amnt value from acc1167 by the ratio and get a number that will then replace the acc1167 amnt value.

for example, sumA = 3750, sumB = 1150. taking these values, sumB/sumA = 0.307. I then replace every value in acc1167 amnt with 0.307*itself, so the final table should look like this:

          acc1167
    ven   job#    amnt
    1167   1      61.4
    1167   2      92.1
    1167   3      30.7
    1167   4      61.4
    1167   5      61.4
    1167   6      46.05

i have tried to use the sum function and and some insert, but i am very new to SQL and have never used sum before and don't know how to call from multiple tables, or how to store a ratio. Ive tried this:

    UPDATE     acc1167
    sum1 = sum amnt1 where ven1 = '1167'
    from accnt
    sum2 = sum amnt
    from accnt
    SET        amnt = sum2/sum1*amnt
    FROM       acc1167