Adding in your head

Hello, and welcome to Myriora Maths! Forty-seven plus thirty-five. Can you do it in your head, with no paper? Today, you will!

Why add in your head? At the shop, you might buy a comic for forty-seven pence, and a drink for thirty-five pence. You won't always have paper, but you'll always have your head!

The trick is to split the numbers into tens and ones. Forty-seven is forty and seven. Thirty-five is thirty and five.

Why does splitting work? Forty-seven is four tens and seven ones. Thirty-five is three tens and five ones. Adding them just puts all the tens together, and all the ones together. Nothing gets lost!

Add the tens first: forty plus thirty is seventy. Then the ones: seven plus five is twelve. Finally, put them together: seventy plus twelve is eighty-two!

Let's try one together. What is twenty-four plus thirty-three? Tens first, then ones. Say your answer out loud!

Twenty and thirty make fifty. Four and three make seven. Fifty-seven! Well done if you said fifty-seven!

Let's try another: twenty-six plus fifty-three. Twenty and fifty make seventy. Six and three make nine. Seventy-nine!

Here's a question that catches lots of people. What is forty-seven plus thirty-five? Some people get seventy-two. But seven plus five is twelve, not two. Twelve is another ten, and two ones. So it's eighty-two!

Your turn! What is thirty-eight plus forty-six? Pick the right card. You've got fifteen seconds, or pause the video. Go!

Time's up! Thirty plus forty is seventy. Eight plus six is fourteen. Seventy plus fourteen is eighty-four! Not seven hundred and fourteen: fourteen has a ten inside it.

Quick review. Split each number into tens and ones. Add the tens, then the ones. Then put them together, and watch for a new ten! See you next time!