There's a great math trick for multiplying numbers. For this trick to work the numbers must start with the same digit and the last digits must add up to ten.
Let's look at an example. The first example is 44x46. Here the two numbers start with the same digit, which is 4. Their last two digits, 4 and 6, add up to 10. What we must first do is add a 1 to 4 and multiply. 5x4=20, so the first number that we write is 20. Next we have to multiply the last two digits, 4 and 6. 4x6=24, so we write 24. Now we have our answer. 44x46=2024.
Let's look at another equation. We can add 88x82. These two numbers also start with the same digits and the last digits add up to 10. 9x8=72 and 8x2=16. This gives us our answer. 88x82=7216.
With 21x29, we first write 6 because 3x2=6. 9x1=9, but we need two digits so we write 09. 21x29=609.
This math trick also works with numbers greater than two digits. Let's use the example of 103x107. 10x11=110, so we write this down. 3x7=21, so we write this down also. Now we have our answer. 103x107=11021.
When two numbers start with the same digit and their last two digits add up to ten, there's a math trick we can use to quickly multiply the two numbers. We simply add one to the first digit and multiply. We write this down and then multiply the last digits of each number and write this down as well. Knowledge of this math trick is very useful for multiplying numbers quickly in our heads.
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