Column subtraction

Hello, and welcome to Myriora Maths! What is four thousand and two, minus one thousand, seven hundred and eighty-six? All those zeros look scary. By the end of this video, they won't be!

Let's start smaller: three hundred and fifty-two, minus one hundred and twenty-seven. Write the bigger number on top, and line up the ones, tens and hundreds. Always start with the ones, on the right.

Two take away seven? We can't do that: two is smaller than seven. So we exchange. Take one ten from the five tens: that leaves four tens. The ten becomes ten ones, so now we have twelve ones. Twelve take away seven is five.

Now the tens: four take away two is two. Then the hundreds: three take away one is two. Three hundred and fifty-two minus one hundred and twenty-seven is two hundred and twenty-five.

Why does exchanging work? One ten is the same as ten ones. Three hundred and fifty-two is three hundreds, five tens and two ones. It's also three hundreds, four tens and twelve ones. It's the same number, just split differently!

Now the scary one: four thousand and two, minus one thousand, seven hundred and eighty-six. Ones: two take away six? We need to exchange. But there are no tens, and no hundreds! So go all the way to the thousands. Four thousands become three. The hundreds get ten. One hundred goes to the tens, so the hundreds have nine, and the tens get ten. One ten goes to the ones, so the tens have nine, and the ones have twelve.

Now every column is easy. Twelve take away six is six. Nine take away eight is one. Nine take away seven is two. Three take away one is two. The answer is two thousand, two hundred and sixteen!

Let's try one together. What is five hundred and three, minus one hundred and sixty-eight? Start with the ones. Can you take eight from three? Say it out loud!

No! So exchange. There are no tens, so take one hundred: five hundreds become four. The tens get ten, then give one to the ones: nine tens, and thirteen ones. Thirteen take away eight is five. Nine take away six is three. Four take away one is three. The answer is three hundred and thirty-five!

Here's a question that catches lots of people. What is fifty-two minus twenty-seven? Some people see two take away seven, and do seven take away two instead. They get thirty-five. But you must always take the bottom digit from the top! Exchange a ten: twelve take away seven is five, and four take away two is two. The answer is twenty-five.

Your turn! What is seven hundred, minus two hundred and fifty-four? Pick the right card. You've got fifteen seconds, or pause the video. Go!

Time's up! Zero take away four? Exchange from the hundreds: seven becomes six, the tens become nine, and the ones become ten. Ten take away four is six. Nine take away five is four. Six take away two is four. The answer is four hundred and forty-six!

Quick review. Start with the ones, and always take the bottom digit from the top. If the top digit is too small, exchange one from the next column. If that column is zero, keep going left until you find one. See you next time!