Why Learn Mental Math?
We all have phones with calculators. So why learn to do math in your head?
Because it helps you every day! It helps you check if your change is correct at the store. It helps you split a bill with friends. It also makes your brain stronger.
If you always use a calculator, you might not notice if you press the wrong button. But if you know mental math, you will know when an answer looks wrong.
Here are 5 easy tricks to help you calculate fast.
1. The Left-to-Right Method
In school, we learn to add from right to left. But when doing math in your head, it is easier to go from left to right.
Example: $47 + 36$
- Step 1: Add the big numbers first (the tens): $40 + 30 = 70$.
- Step 2: Add the small numbers (the ones): $7 + 6 = 13$.
- Step 3: Add them together: $70 + 13 = 83$.
This way, you get the big part of the answer first. It is faster and easier to remember.
2. Make Numbers "Friendly"
Some numbers are hard to add, like 9 or 47. Numbers ending in 0 (like 10, 50, 100) are "friendly" and easy.
Trick: Change the hard number to a friendly number, do the math, then fix it at the end.
Example: $98 + 47$
- 98 is hard. 100 is easy.
- Step 1: Pretend 98 is 100 (we added 2).
- Step 2: $100 + 47 = 147$.
- Step 3: Take back the 2 we added: $147 - 2 = 145$.
Answer: $145$.
3. Subtracting from 1,000
Here is a cool trick to subtract a number from 1,000.
The Rule: Subtract every number from 9, except the very last one. Subtract the last one from 10.
Example: $1,000 - 648$
- 6: $9 - 6 = 3$
- 4: $9 - 4 = 5$
- 8: $10 - 8 = 2$ (Last one subtracts from 10)
Answer: $352$.
4. Multiplying by 11
Multiplying a two-digit number by 11 is like magic.
Example: $35 imes 11$
- Take the two numbers: 3 and 5.
- Add them: $3 + 5 = 8$.
- Put the 8 in the middle: 385.
That's it! If the middle number is bigger than 9, just carry the 1 to the first number.
5. Double and Half
This trick helps when multiplying. If you double one number and cut the other in half, the answer stays the same.
Example: $16 imes 15$
- Cut 16 in half $ ightarrow$ 8.
- Double 15 $ ightarrow$ 30.
- New problem: $8 imes 30$.
- This is easy: $8 imes 3 = 24$, then add the zero.
- Answer: $240$.
Keep Practicing!
Like sports or video games, you get better at math by practicing. Try using one of these tricks today. You will be surprised how fast you get!
Want to try it out? Go to our Speed Challenge now!