Math Shortcut: Squaring Numbers from 50 to 70

We have already learned how to square numbers from 80 to 100. In this post, we are going to show a shortcut on squaring numbers from 50 to 70. Here are example and the steps.

Example 1: 522

Step 1: Consider how far is 52 from 50. The answer is 2.

Step 2: Add 2 to 25. This gives us 27, 2 is the thousands and 7 the hundreds digit. This gives us 27xx where xx are the tens and ones digits.

Note: The number 25 comes from squaring the tens digit which is 5. I will explain this in the next post.

Step 3: To get xx, we square the ones digit of the given which is 2. This gives us 4. Since we only have 1 digit, we put 0 before 4, giving the value of xx as 04.

Therefore, 522= 2704 Continue reading

Mathematical Magic at America’s Got Talent

Last year, there was one episode of mathematical magic at America’s Got Talent. It was supposed to involve one imaginary friend who creates a zodiac calendar based on an audience choice of number.

Since it’s hard to explain, just watch and see. Honestly, I have no idea how he did it. 
You can share what you think by posting your comments below.

Multiplying Large Numbers by 11

The last post about multiplying by 11 only works for two-digit numbers. There’s also a simple trick for multiplying by 11 for larger numbers, and it’s very easy! Let’s have an example of 236 × 11.

First, we write the problem like this:

0236 × 11

We write a zero in front of the number we are multiplying. You’ll see why in a moment. To find the product when multiplied by 11, we simply add each digit to the digit on its right, starting with the units digit.

The units digit is 6, but there is no digit to the right of 6, so we add 0:

6 + 0 = 6

So the last digit of our answer is 6. Let’s write that down:  Continue reading

The Idea Behind the 1089 Math Trick

In the previous post, we have learned about the 1089 math trick. In this post, we are going to learn why the math trick works. Recall that the math trick has the following steps:

1.) Write a 3-digit number where the digits are decreasing.

2.) Reverse the digits of the number.

3.) Subtract the result from (2) from the original number in (1).

A 3-digit number, write the digits abc has value 100a + 10b + c. For example, the number with digits 347 has value 100(3) + 10(4) + 7.

In Step 1, we write the number 100a + 10b + c where a >= b and b >= c.

In Step 2, if we reverse the digits, it will become 100c + 10b + a.  Continue reading

The 1089 Math Magic

Here is a little trick.

1.) Write a 3-digit number whose digits is decreasing. For example, 421.

2.) Next, reverse the order. The new number now is 124.

3.) Subtract the original number from the reversed number.
421 – 124 = 297

4.) Add the answer in (3) to the reverse of itself.
297 + 792 = 1089.

Let’s try another example.

First step, let’s choose 843.

Next, we reverse its digits: 348.

We subtract: 843 – 348 = 495.  Continue reading