Transcript:

How to multiply triple digits by double digits. I'm Bon Crowder with MathFour.com, and we're talking about multiplication using triple digits and double digits. The traditional way of doing this is to stack the triple digit number on the top and put the double digit number on the bottom to multiply. Then we multiply the 1s place by the entire triple digit number. So 8 x 2 is 16 and carry the 1, 8 x 5 is 40 + 1 is 41 and carry the 4, 8 x 3 is 24 + 4 is 28. Now we have to multiply by 4 but we're not just multiplying by 4, we're multiplying by 40 so I need to compensate by putting a little placeholder here, so 4 x 2 is 8, 4 x 5 is 20. I need to carry my 2 but I have to be careful not to get it mixed up with the other guys, 4 x 3 is 12 + 2 is 14 and then I add those 2, so I have 6, 9, 8, 6, 1 put a comma to make it look pretty. The reason why we can do this is because 352 x 48 is the same as 352 x 40 + 8 and that's what we did. This is the x 8 and this is the x 40 and here is what it looks like when you jump over some day into algebra. You distribute those 2 and if you multiply 352 x 40 and 352 x 8 and then add those together, guess what you're going to get? That guy right there. I'm Bon Crowder with MathFour.com and that's how you multiply a triple digit number by a double digit number.