HELP WITH CALCULATION

Hi All,

I am new here and finding  it difficult to get around this query.

i am trying to do the below

original amount =  DIVIDE ([ACTUAL NET PREMIUM RECEIVED], [RATE OF EXCHANGE])  * COUNT(POLICY[POLICY_NUMBER)

but i am not getting the right result. 

in summary, if i  divide between (actual net preview) and (rate of exchange) and the result  = 20 and policy number appears 10 times, i want to be able to multiply 20 * 10 .

i also try to do it seperately   = original amaount * count(policy[policy number) still not getting it right.

basically, i want to do a group by on policy number 

policy number     

aaaa

aaaa

aaaa

aaaa

bbb

bbb

bbb

aaaa

cccc

cccc

so i want to count number of policy number then multiple it by the division result. 

Any help will be grateful