Adding double-digit numbers can seem difficult for some students. But, this Khan Academy video makes this process clear in a developmentally sound way. Students watch as 'Sal' adds the number 46 to 43. He references each number by its place value; so 6 +3 is 6 ones + 3 ones, and 4+4 is 4 tens + 4 tens or 40+40. The concept of place value is key in understanding re-grouping and double-digit multiplication. Seeing place value in a math application really reinforces the concept.