=SUMIF(WeekRange,Week,SumRange)

jeremy via OfficeKB.com wrote:
This formula

=SUMPRODUCT((MONTH(AO9:AO272)=1)*(AM9:AM272))

sums up the weight per month. How would I sum up the weight per week--the
weeks ar entered in anywhere between 1 week and 15 weeks....ie add up all
the weight for those that took 1 week, all the weight that took too weeks etc.
....

There's two columns: weeks and weight.....

thanks