How many coupons in a deal does a consumer actually buy?

I try to answer this question by studying 206,990 transactions of 1,395 deals which are sold on a Vietnam group-buying site in 12 months. There are about 290 deals, each of which has sold over 500 coupons.

A transaction, in this context, records the total number of coupons which a consumer bought in a deal. For example, if Mr. A bought coupons of a deal at different dates (e.g., 5 coupons on this Monday and 4 coupons more on this Friday), then one transaction would be recorded that Mr. A had bought 9 coupons of that deal.

The limitations of this calculation:
1/ Only one website is observed. 

2/ If a deal sold over 500 coupons, only 500 most recent ones would be observed.

3/ Keep in mind that a same consumer may buy other deals; so this is, in fact, a frequency measurement of how many coupons a consumer bought in a deal.

Results:
- 61% of the transactions in which a consumer bought 1 coupon only.

- 25% of the transactions in which a consumer bought 2 coupons.

- 13% of the transactions in which a consumer bought from 3 to 10 coupons.
- 01% of the transactions in which a consumer bought over 10 coupons.

Data Source: http://docs.com/GJKF