You are selling a mobile app for $10 per user per month. if you get 7 users every month starting with 10 in the first month. how much money do you have in 1 year?

Selling price of app per user = $10 per month

Total no. of user in first month = 10

To tal no. of user added per month = 7

We have to find how much money is earned in one year

So the formula is n/2 * (2a +(n-1)d)

Here we have n = 12 which is total no. of months

a = 100 , which is money earned in one month

d = 70 , which is increase in money earned per month

So money earned in a year comes out to be 5820