SUM of clumps of different items sold

Guys and Gals,
Please be so kind and help with a formula for the following dillemma:

I have a 7000 row spreadsheet of items sold over the past 6 months. I sorted them by their SKU, but some of them sold in multiple qty in a given day.

What is a formula to calculate the total qty of each SKU sold?

Example:
Column A = SKU 001
Column B = Qty Sold in a particular purchase (most have 1, but some are 2 or 3 or 4, etc.)
Column C, (Row 10) = Total where I would like to come up with a number for columns 1-10 (for example).

next item:
Column A = SKU 002
Column B = Qty Sold in a particular purchase (most have 1, but some are 2 or 3 or 4, etc.)
Column C, (Row 17) = Total where I would like to come up with a number for columns 11-17 (for example).

P.S. Rows per SKU vary (they represent each purchase of a given item)

THANK YOU INFINITELY IN ADVANCE FOR A SOLUTION