Calculating 2 weighted averages in one equation

Hello Everyone,

this is my first post in your topic, am having a big time problem calculating the weighted average in my below sample of Data:

Lifetime Users # Occurrences

1 Month 50000 24

2 Months 10000 24

3 Months 5000 24

4 Months 2500 24

5 Months 1500 24

As you can see the sample includes data about the lifetime of users and the number of users as well as the occurences of each lifetime period. the question is how can i calculate the average of user lifetime according to this sample.

Note: Am sorry, if this topic is not posted in the right section, but am not really an expert at statistics.

Waiting for your replys.

Thanks.