Hi, need help with writing a formula

[jay10]

Here is a sample of my data:

date_sign_up	customer_id	product_name	marketing_channel	City
4/17/15 13:11​	71041​	Classic - 3 meals per week for 2 people	Search Engine Marketing	San Diego
4/14/15 11:32​	103289​	Classic - 3 meals per week for 2 people	Newsletters (internal)	Los Angeles
4/14/15 9:53​	107746​	Classic - 3 meals per week for 2 people	Newsletters (internal)	Los Angeles
4/14/15 16:08​	157441​	Classic - 3 meals per week for 4 people	Newsletters (internal)	San Francisco
4/18/15 8:04​	158646​	Classic - 3 meals per week for 2 people	Newsletters (internal)	San Diego
4/18/15 15:41​	178843​	3 Meals (vegetarian) for 2 people	TV / Radio Advertising	Miami
4/15/15 9:45​	179297​	Classic - 3 meals per week for 2 people	Newsletters (internal)	Philadelphia

I need to write a formula that answers this question:

How many customers purchased more than 1 product? Solve with 1 formula and show the formula you used.

 

[CJ_London]

sounds like homework to me - suggest investigate using the find duplicates wizard

 

[jay10]

sounds like homework to me - suggest investigate using the find duplicates wizard

I did that and found it of course, but this specifically asks for a formula

 

[arnelgp]

use:

=COUNTIF(B:B,"="&B2)

 

[CJ_London]

Ah - didn't notice this was an excel question