Don’t be intimidated by numbers, sometimes they are much simpler than they look.Below we introduce 10 arithmetic tips Very simple so that you can be the center of attention at a “party” with mathematicians.
#10.Multiply by 11
We all know that when we multiply any number by 10, we simply add a zero at the end of the number to get the result. Did you know there’s an equally simple trick for multiplying by 11?
Take any two digits and imagine there is a space between them. In this example we will use 72:
7_2
Now put the sum of these two numbers into the blank space:
7_ (7+2) _2
It’s that simple, you get the product of 11 x 72: 792
If the blank sum results in a two-digit number, you must take the first digit of the result and add the amount to the first digit of the original number. Let’s use the number 93:
9_3
9_ (9 +3) _3
9_ (12) _3
(9+1)_2_3
1023
It never fails!
#9. Quick Square
If you need to know the square of any two-digit number ending in 5, you can use this simple trick. Multiply the first digit itself by 1 and add 25 at the end. That’s it.
352 = ( (3x (3+1) ) & 25
1225
#8. multiply by 5
Memorizing the 5 times table is very simple, but when we have to deal with larger numbers, things get more complicated, don’t they? This trick is very simple. Take any number and divide it by 2 (i.e. half). If the result is an integer, 0 is added at the end. Otherwise, eliminate the point (place the last 5 points). It also never fails. Let’s start with 3024:
3024 x 5 = (3024/2) and 0 or 5
3024/2 = 1512 & 0
15120
Let’s try again:
63 x 5 = (63/2) and 0 or 5
31.5 (ignore this and leave only the 5 already at the end)
315
#7. Multiply by 9
It’s very simple. To multiply any number between 1 and 9 by 9, you must hold your hands out in front of you. Then, press only the finger you want to multiply by 9, the finger that exactly corresponds to the number you want to multiply. For example, if you want to multiply 9 by 4, place your ring finger down. Count the fingers before the one on the left (3 in this case) and then the fingers on the right (6 in this case).
Answer = 36
#6. Calculate 15%
If you need to calculate 15% of any number, it’s easy. Just divide that number by 10 and add half of that result to yourself. The equation is much more complex than the trick itself. Let’s illustrate with the number 300:
15% of 300 = (300/10) + ((300/10) / 2)
30 + 15 = 45
#5. Multiply by 4
This seems simple and seems obvious. But for many people this is not the case. This is multiplied by two and multiplied by two again.
66 x 4 = (66 x 2) x 2
132 x 2 = 264
#4. Multiplication is difficult.
If you must multiply large numbers and one of them is an even number, just divide the even side by 2 and multiply the odd side (or the longer side) by 2.
64 x 125 is equivalent to:
32 x 250, equivalent to:
16 x 500, equivalent to:
8 x 1000 = 8000
#3. Divide by 5
In fact, dividing a large number by 5 is very simple. All you have to do is multiply by 2 and move the decimal around. We use the number 3250 to illustrate.
3250/5 = 3250 x 2 move the decimal point one place to the left
6500 = 650.0
650
Oh fine:
41/5 = 41 x 2 Decimal point moved one place to the left
82 = 8.2
#2. Subtract any number from 1000
To subtract any number from 1000, use this basic rule. Subtract each digit from 9 except the last digit from 10.
1000 – 723
Step 1: 9 minus 7 = 2
Step 2: 9 minus 2 = 7
Step 2: 10 minus 3 = 7
Answer: 277, absolutely correct.
#1. Various multiplication rules
Multiply by 5: Multiply by 10 and divide by 2.
Multiply by 6: Sometimes it’s easy to multiply by 3 and then by 2.
Multiply by 9: Multiply by 10 and subtract the original number.
Multiply by 12: Multiply by 10 and add twice the original number.
Multiply by 13: Multiply by 3 plus 10 times the original number.
Multiply by 14: multiply by 7, then multiply by 2
Multiply by 15: Multiply by 10 and add 5 times the original number.
Multiply by 16: Can be four times multiplied by 2. Or multiply by 8 and then multiply by 2.
Multiply by 17: Multiply by 7 plus 10 times the original number.
Multiply by 18: Multiply by 20 and subtract twice the original number.
Multiply by 19: Multiply by 20 and subtract the original number.
Multiply by 24: multiply by 8, then multiply by 3.
Multiply by 27: Multiply by 30 and subtract 3 times the original number.
Multiply by 45: Multiply by 50 and subtract 5 times the original number.
Multiply by 90: Multiply by 9 and add zeros to the right.
Multiply by 98: Multiply by 100 and then subtract twice the original number.
Multiply by 99: Multiply by 100 and subtract the original number.