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
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
In the previous post, we have learned how to square 2-digit numbers mentally. In this post, we learn specifically another strategy on how to square numbers from 80 to 100.
Steps in Squaring Numbers From 80 to 100
Step 1: Subtract the number from 100.
Step 2: Square the difference.
Step 3: Subtract the result in 1 from the given number.
Step 4: If the result is a 2-digit number, append the result in 3 to the result in 2 (see Examples 1 and 2). If the result is a 3-digit number, add the hundreds digit to the ones digit of the given number and then append the 2 digits (see Example 3).
Example 1: 942
Step 1: We subtract 94 from 100. That is, 100 – 94 = 6.
Step 2: Square 6 which equals 36. Continue reading
Squaring large numbers is not an easy task to do. However, using a right strategy and with constant practice, it can be done. Below is one method that you might want to try. This strategy only requires three steps and a lot of focus. 😉
Steps on How to Square 2 Digit Numbers Mentally
(1) Look for the difference between the number and the nearest multiple of 10. For example, we would like to square 42. The nearest multiple of 10 is 40, so the difference is 2.
(2) Multiply the following
(the number + difference) × (the number – difference).
So, in this case, (32 + 2)(32 – 2) = 34 × 30. Continue reading
We have learned how to multiply 2-digit by 1-digit numbers mentally and in this post, we are going to discuss its corresponding method in division. Division seems to be the most difficult operation in mental calculation, but with the right strategy, it can be done. In the discussion, we will start with easy examples and then proceed to more complicated examples later.
Example 1: 52 ÷ 4
We can separate 52 into 40 and 12. Then, we can divide 40 by 4 which is equal to 10. Next, we can divide 12 by 4 which is equal to 3. So, we have 10 + 3 = 13.
40/4 = 10
12/4 = 3
So, the answer is 10 + 3 = 13. Continue reading