It is complicated to say a number since it depends on a lot of parameters. What you should do first is estimate your conversion rate (as I have read in some places, the average conversion rate in Android is 10%).
That 10% is the people who click on your ad and maybe (or maybe not) buy the product, so you will earn more from them (since you will earn more for someone clicking your ad that someone seeing your ad, obviously).
Now, you have another 90% of people who just see your ads. Let's say you have 10K different users, so 10K * 90% = 9K
You need to know how much people of that percentage would be connected to the Internet (if they are not connected, ads won't show!). Let's say around 60% (I don't know the percentage, but most people have the mobile connected to the Internet all day, so let's say that number). So, 9K * 60% = 5.4K
Let's say that this is the worst case, and everyone who download the app but don't click on your ads (the initial 90%), just use your app few minutes and uninstall it. So, let's say they are around 5 minutes using your app before uninstalling it.
And finally, let's say you refresh your ads twice per minute (so you show a new ad every 30 seconds, 2 impressions per minute)
You would have 5.4K users * 5 minutes in the app * 2 impressions per minute = 54000 impressions
Now you have to know your CPM, let's say it is around $3 per 1K impressions. And to simplify maths, let's say you get 100% fill rate too, so:
54000 impressions * $3 per 1K impressions (3/1K) * 100% fill rate = $162
That would be what you earn from users who don't click on your ads, so you have to add what you earn for users who click on your ad.
Please, remember that this is just general information, it is not accurate, just based on my own experience and opinions I have read on the Internet. Also, remember all these rates depends on a lot of parameters like the country where the user is, app type, network and many many more. And also remember it is a bad case since most of your users would be uninstalling your app and just using it for 5 minutes.