Month in Review – May 2015

Welcome math enthusiasts. Starting this month, we will have our month in review every end of the month.  For those who missed some posts this month, we have learned the following.

To see all the posts arranged by month, you can visit the Post List page.  You may also want to visit the newly created category menus at the top of the page.

Enjoy learning and have a nice weekend everyone.

Math Shortcut: Squaring Numbers from 30 to 50

In the previous post, we have learned an interesting math shortcut on squaring numbers from 50 to 70. Before we explain why the shortcut works, we first continue this series by learning a shortcut on squaring numbers from 30 to 50. Notice that the steps are almost similar.

Example 1: 472

Step 1: First, consider how far is 47 from 50 (the base). This means that we want 50 – 47 = 3.

Step 2: Subtract 3 from 25. This gives us 23. This gives us 2 as the thousands and 3 as the hundreds digit of the product. That is, 472 = 23xx where xx are the tens and ones digits.

Note: The number 25 comes from squaring the tens digit of 50 (the base).

Step 3: To get xx, we square 3, the number we subtracted in Step 2. This gives us 9. Since xx represents a 2-digit number, we add 0 to make it 09.

Therefore, 472= 2209  Continue reading

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