Please find some tips to math questions easy. These tricks are easy to remember to do all match calculations.
Everybody knows that if we want to multiply with any number with 10 or 100 you just add one or two 0 after that number. E.g. if you multiply 39 with 10, you just add one 0 to 39 to become 390.
Here goes, the first one is easy.
1. To multiply any number by 4 all you do is double it, and then double it again.
Example: 16 X 4.
First Double the 16: 16 X 2 = 32
Then Double the 32: 36 X 2 = 64
2. To multiply any number by 5, just divide the number by 2, and then re-affix any necessary decimal points or zeroes.
Example: 56 X 5.
First Divide: 56 ÷ 2 = 28.
Then Make sense? 18 is obviously too small to be the answer to 56 X 5. It's clear that the answer is somewhere in the 100s. So you add a zero to the 18 and you have the correct answer – 280.
3. To multiply by 9
An easy one - Simply multiply the number by 10, and then subtract the number itself from the result.
Example: 18 X 9
First Multiply: 18 X 10 = 180.
Then Subtract: 180 - 18 = 162
4. To multiply any two-digit number by 11.
First, write the number, leaving a space in between the two digits. Then insert the sum of the two digits in between the two digits themselves.
Example: 54 X 11.
First Write down the two digit number, leaving a gap between the two digits: 5 _4.
Then add the two digits: 5+4 = 9.
Then Insert the sum between the 3 and the 4, which gives you the answer – 594.
You will have to ‘carry’ when the sum of the two digits exceeds 9.
Example: 48 X 11.
First Write 4 _8.
Then add the two digits: 4 + 8 = 12.
Then because the two digits total more than 9, you must insert the 2, which gives you 428,
Then ‘carry’ the 1 (add it to the 4), giving the answer - 528.
5. To multiply any number by 25,
To do this, just divide the number by 4, and then add any necessary decimal points or zeroes.
Example: 36 X 25.
First. 36 ÷ 4 = 9
Then. 9 and 90 both seem too small to be the correct answer to 36 X 25.
Then. Add two 0 to the 9 giving the correct answer - 900.
6. Divide number by 25
Here, you multiply the number by 4, and then add any necessary decimal points or zeroes.
Example: 500 ÷ 25.
First ignore the zeroes and multiply 5 X 4 = 20.
7. To multiply any two-digit number by 99
First, subtract 1 from the number to obtain the left hand part of the answer. Then, subtract the number from 100 to get the right hand part. Sounds a bit complicated, I know. Look at the example below and it will become clear.
Example: 15 x 99.
First Subtract: 15 – 1 =14. (Left- hand part of the answer).
Then Subtract. 100 – 15 = 85. (Right-hand part of the answer).
Then Put both parts together: 1,485 is the answer.
8. To multiply any two-digit numbers from 11 to 19.
Example. – 18 x 16.
First Take the whole of the higher number: (18) and add to the second digit in the smaller number: 18 + 6 = 24.
Then Add a zero to the end of the answer (multiply by 10): 240.
Then Multiply the second digits of the original sum: 8 X 6 = 48 and add it to the answer from step 2: 240 + 48 = 288
Example 2. – 430 X 9
First Ignore the zero and multiply: 43 X 10 = 430.
Then Subtract: 430 - 43 = 387
Then Make sense? It's obvious that 387 cannot be the answer as it's lower than the number you are multiplying. Add a nought and you have the correct answer - 3,870
