I saw this math shortcut trick on the internet but they did not take it far enough. They said it only worked with the #5 but I have discovered that it works with numbers 2-9 (#1 should not be necessary).
It is multiplying 2 like numbers by a single number or even by a double number if it meets one simple requirement.
Here are some examples with explanation.
44x5=? In this case you multiply 4x5 (20) and put the answer like so 2(space)0.
Next the add the 2 and 0 (2+0) and put that between as the middle number.
So the answer to 44x5 is 220.
Another example: 88x9. 8x9-72. 7(space)2. 7+2=9. So, 88x9=792.
Last example before I show you a little advanced step.
99x6. 9x6=54. So the answer is 594.
Now for the little bit advanced method. When you add up the 2 numbers after that first multiplication and it comes out to more than 9.
Example: 88x7. 8x7=56. 5(space)6. 5+6=11. So instead of inserting the 11 between the 5 and the 6 you add first 1 (in the ten spot) to the 5 (making it a 6). Then you insert the other 1 between the (now) 6 and the other 6. Giving you the answer of 616. So 88x7=616.
Another example:66x8. 6x8=48. 4+8=12. So 4(space)8 then add 1 to the 4, so 528. 66x8=528.
Last example before a quick note and a little bit on using double digits.
88x8. 8x8=64. 6+4=10. 6+1=7. 88x8=704.
Quick Note: Any double digit, double numbers times nine will always come out to “9” as the middle number. So if you see, for example 33x9, you know to just put a ‘9” between the answer to 3x9 (27). 33x9=297. So 55x9(5x9=45) so 55x9= 495, 88x9=792 and so forth.
Double digits with double numbers. These are all much easier if you put them in this format. You can actually solve the equation on one line this way.
These are just as easy as the single digits and much faster than what was taught in school (at least when I went to school). FYI: This process only works if one of the numbers is a double number (22, 33, 77 etc).
An example would be 33x12. You simply do 3x1 (3) and 3x2 (6) and put it down as 3 6. Then add the 3 and 6, 3+6=9. Put the 9 in the space. Answer: 396.
18x11 = 1 8. 1+8 (9). Answer: 198.
The majority of these double digit equations will have double digit answers when you add. Here is how you handle the situation when that occurs.
The process works the same way as the previous examples except you have one extra step to add.
Example: 88x39=? 8x3 (24) and 8x9 (72). Start at the back and put the 2 (in 72) as your last number. Then you add the 7 to the 24 (7+24) (31). So now you have 31 2. Add 31+2 (33). The 3 in the ones slot is your 2nd to last digit in your solution. The 3 in the tens spot is added to the 31 (now 34). Answer: 3432
That seems complicated but it’s actually very simple and when you write the problem on paper, you’ll see how simple.
Another example: 66x48=? Start with 6x8 (48). Put down the 8 (last digit). Carry the 4. Now do 6x4 (24) + 4 (the carried 4) = 28. So now you have 28 8. Add 28+8 (36). Put down the 6 and add the 3 to the 28. That gives you the answer, 3168.
44x78= 4x8 (32) and 4x7 (28). Put down the 2 (from 32 as the last number). Carry the 3. 3+28 (31). So now you have 31 2. Add 31+2 (33). Put down the 2nd 3. Add 1st 3 to 31 (34). Answer 3432.
77x39= 7x9 (63), 7x3 (21), 21+6 (27), 27+3 (30). Answer: 3003.
44x58= 4x8 (32), 4x5 (20), 20+3 (23), 23+2 (25). Answer: 2552.
Sure you could use a calculator and figure these out much quicker, but where’s the fun in that?
And you won’t always have a calculator around.