THE ELEVEN TRICK:
This is our absolute FAVORITE multiplication trick here at themathlab.com. It is a real "show stopper". People will think you are unbelievably smart when they see you do this one.
To multiply any single digit number by eleven you just write the digit twice. Ex. 7x11=77.
The impressive power comes when you can take any two, three, or four digit number times eleven, and get the answer IN YOUR HEAD without showing a scrap of work.
Ex. 23 x 11 = 253 instantly!
Here's how you do it.
Since you are multiplying eleven by 23, your answer will have a 3 on the right and a 2 on the left and the SUM of 2 and 3, which is five, in the middle. Just think of it as pulling the 2 and 3 apart and inserting their SUM in the middle.
Believe it or not, it's just that easy. Any two digit number times eleven can be done like that. If the sum in the middle is 10 or greater just put the ones digit of the sum in the middle and make the left digit bigger by one.
Ex. 48 x 11 = 528 (Think: eight goes on the right, 4+8=12 so write down the two in the center and carry the one to add to the 4 making the leftmost number now a 5.)
Ex. 99 x 11 = 1089
Here. Try a few yourself. Click on the ? to see if you are correct. *This only works in Internet Explorer.
This method even works for longer numbers. You place the ones digit in the ones spot and simply continue adding pairs across the number from right to left, carrying as needed until the leftmost digit or that digit plus one more is placed on the left side of the answer.
Here. Take a look at couple examples.
Ex. 349 x 11 = 3839 (Think: place the nine on the right first, then add 4+9=13. So we place the three beside the nine, carry the one and add it to 3+4 giving us a total of 8. We write the eight to the left of the three and then since there was nothing to carry, we finish the number by placing the 3 in the leftmost spot.)
Ex. 978 x 11 = 10,758 (Here we have to carry the whole way across the number. That's why the leftmost digit is not nine but 10.)
Try your hand at a few. If you get them all correct, go ahead and tackle the Password Clues.
Remember to click the ? to see if you are correct.
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