Tricks and Tips for Doing Math in Your Head
It doesn’t take a math teacher to realize that there are a lot students and parents who don’t like math. Math problems can be intimidating, especially when they involve large numbers. Learning how to quickly do math can help students gain more confidence, understand math better, and excel in advanced classes.
Here’s a refresher for those who have to teach them.
10 tricks for doing fast math
Here are 10 quick math strategies that students (and adults) can use. You can use these strategies to solve math problems in your head. These strategies will allow students to solve math problems they used to be afraid of.
1. Add large numbers
It can be hard to add large numbers in your head. This method simplifies the process by making all numbers a multiple 10. Here’s an example:
644 + 238
These numbers can be difficult to manage, but it is possible to simplify them by rounding them up. So 644 becomes 654, and 238 becomes 244.
Add 650 to 240. The sum is 890. The answer to the original equation must be found by determining how much we added to these numbers in order to round them up.
650 – 644 = 6, and 240- 238 = 2.
Add 6 and 2 together to get 8
To find the solution to the original equation, you must subtract 8 from 890.
890 – 8 = 882
The answer to 644 +238 can be found at 882
2. Additions starting at 1,000
To subtract large numbers from 1,000, here’s an easy rule: Take every number but the last 9 and subtract the last number from 10.
Take, for example:
1,000 – 556
Step 1: Add 5 to 9 = 4.
Step 2: Add 5 to 9 = 4.
Step 3: Add 6 to 10 = 4.
It is 444.
3. Multiply any number 5 times
Multiplying 5 with an even number will give you the quick answer.
Example: 5 x 4.
- Step 1: Multiply the number by 5 and then divide it in half. This makes the number 4 the number 2.
- Step 2: To find the answer, add a zero to the number. The answer in this example is 20.
5 x 4 = 20
Multiplying an odd number by 5 results in a slightly different formula.
Consider 5×3.
- Step 1: Add one to the number multiplied with 5, in this case the number 3 is the number 2.
- Step 2: Now, divide the number 2 by 2, making it 1. Add 5 to the last digit. The answer is 15.
5 x 3 = 15.
4. Tricks for division
These numbers can quickly be used to determine if a number can evenly be divided.
- If the number ends in 0, then 10
- 9 when all the digits have been added together, and the total is equally divisible by 9.
- 8 if the three last digits of the number are equally divisible by 8 (or are 000).
- 6. If it is an odd number, the answer can be added together to give the evenly divisible number of 3.
- If it ends in 0 or 5, then 5
- If it ends in 00, or a two-digit number that is equally divisible by 4, then 4
- When the digits of the total are added, the result is equally divisible by the number 3.
- If it ends in 0, 2, 4, 6 or 8, then 2
5. Multiplying by 9
This simple method can be used to multiply any number by 9. This is how it works:
Let’s take the 9×3 example.
Step 1 – Subtract 1 from 9.
3 – 1 = 2
The answer to the equation is 2 – the number 2.
Step 2 : Subtract this number from the number 9.
9 – 2 = 7
The second number in the equation is 7, which is the number 7.
Also, 9 x 3. = 27
6. 10 and 11 times tricks
To multiply any number by 10, add a zero at the end. For example, 62×10 = 620.
You can also multiply any two-digit number by 11 using an easy trick. It’s here:
11 x 25
Add a space between each digit of the original two-digit number. This example shows that the number 25 is.
2_5
Add these two numbers together, and place the result in the middle.
2_(2 + 5)_5
2_7_5
The answer to 11×25 is 275.
If the numbers in center add up to a number that has two digits, insert another number and add 1 to it. This is an example of the equation 11×88.
8_(8 +8)_8
(8 + 1)_6_8
9_6_8
The answer to 11×88 is 968
7. Percentage
It can be difficult to find a percentage of something, but if you think about it in the right terms it will be easier to understand. This is how you can find out what 5% of the number 235 is.
- Step 1: Move decimal point one place over, 235 becomes 235.
- Step 2: Divide 23.5 times by 2, and the answer will be 11.75. This is the same answer as the original equation.
8. Quickly divide a two-digit number ending in 5 by simply adding it up.
Let’s take the number 35 for an example.
- Step 1: Add 1.
- Step 2: Add a 25 at its end.
35 squared = [3x (3 + 1)] and 25
[3 x (3 + 1] = 12
12 & 25 = 1225
35 sq. = 1225
9. Multiplication is difficult
Multiplying large numbers should be done in two steps: Divide the first number by half and then multiply the second number. This will quickly solve your problem. Consider, for example,
20 x 120
Step 1: Divide 20 by 2. This equals 10. Step 1: Divide the 20 by 2, which equals 10.
Add the two answers to your equations.
10 x 2400 = 2400
The answer to 20×120 is 2,400.
10. Multiply numbers that end with zero by multiplying them
Multiplying numbers ending in zero is quite easy. This involves adding the zeros to the end of the numbers and multiplying them. Consider:
200 x 400
Step 1: Multiply 2 times 4
2 x 4 = 8.
Step 2: Add all four zeros following the 8
80,000
200 x 400 = 80,000
These quick math tricks will help students and teachers to improve their math skills, and make them feel confident in their understanding of mathematics.