Addition 1
http://www.khanacademy.org/math/arithmetic/addition-subtraction/v/basic-addition
Addition 2
http://www.khanacademy.org/math/arithmetic/addition-subtraction/v/addition-2
Addition 3
http://www.khanacademy.org/math/arithmetic/addition-subtraction/v/addition-3
Addition 4
http://www.khanacademy.org/math/arithmetic/addition-subtraction/v/addition-4
Level 2 Addition
http://www.khanacademy.org/math/arithmetic/addition-subtraction/v/level-2-addition
Subtraction 1
http://www.khanacademy.org/math/arithmetic/addition-subtraction/v/basic-subtraction
Subtraction 2
http://www.khanacademy.org/math/arithmetic/addition-subtraction/v/subtraction-2
Subtraction 3
http://www.khanacademy.org/math/arithmetic/addition-subtraction/v/subtraction-3---introduction-to-borrowing-or-regrouping
Subtraction word problems
http://www.khanacademy.org/math/arithmetic/addition-subtraction/v/subtraction-word-problem