Top 10 Maths tricks Every Student Should See
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1. The 11 Times Trick
We all know the trick when multiplying by ten – add 0 to the end of the number, but did you know there is an equally easy trick for multiplying a two digit number by 11? This is it:
Take the original number and imagine a space between the two digits (in this example we will use 52:
5_2
Now add the two numbers together and put them in the middle:
5_(5+2)_2
That is it – you have the answer: 572. If the numbers in the middle add up to a 2 digit number, just insert the second number and add 1 to the first:
9_(9+9)_9
(9+1)_8_9
10_8_9
1089 – It works every time.
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2. Quick Square
If you need to square a 2 digit number ending in 5, you can do so very easily with this trick. Mulitply the first digit by itself + 1, and put 25 on the end. That is
all!
25 = (2x(2+1)) & 25
2 x 3 = 6
625
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3. Multiply by 5
Most people memorize the 5 times tables very easily, but when you get in to larger numbers it gets more complex – or does it? This trick is super easy.
Take any number, then divide it by 2 (in other words, halve the number). If the result is whole, add a 0 at the end. If it is not, ignore the remainder and add a
5 at the end. It works everytime:
2682 x 5 = (2682 / 2) & 5 or 0
2682 / 2 = 1341 (whole number so add 0)
13410
Let’s try another:
5887 x 5
2943.5 (fractional number (ignore remainder, add 5)
29435
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4. Multiply by 9
This one is simple – to multiple any number between 1 and 9 by 9 hold both hands in front of your face – drop the finger that corresponds to the
number you are multiplying (for example 9×3 – drop
your third finger) – count the fingers before the dropped finger (in the case of 9×3 it is 2) then count the numbers after (in this case 7) – the answer is 27.
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5. Multiply by 4
This is a very simple trick which may appear obvious to some, but to others it is not. The trick is to simply multiply by two, then multiply by two again:
58 x 4 = (58 x 2) + (58 x 2) = (116) + (116) = 232
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6. Calculate a Tip
If you need to leave a 15% tip, here is the easy way to do it. Work out 10% (divide the number by 10) – then add that number to half its value and you have
your answer:
15% of $25 = (10% of 25) + ((10% of 25) / 2)
$2.50 + $1.25 = $3.75
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7. Tough Multiplication
If you have a large number to multiply and one of the numbers is even, you can easily subdivide to get to the answer:
32 x 125, is the same as:
16 x 250 is the same as:
8 x 500 is the same as:
4 x 1000 = 4,000
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8. Dividing by 5
Dividing a large number by five is actually very simple. All you do is multiply by 2 and move the
decimal point:
195 / 5
Step1: 195 * 2 = 390
Step2: Move the decimal: 39.0 or just 39
2978 / 5
step 1: 2978 * 2 = 5956
Step2: 595.6
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9. Subtracting from 1,000
To subtract a large number from 1,000 you can use this basic rule: subtract all but the last number from 9, then subtract the last number from 10:
1000
-648
step1: subtract 6 from 9 = 3
step2: subtract 4 from 9 = 5
step3: subtract 8 from 10 = 2
answer: 352
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10. Assorted Multiplication Rules
Multiply by 5: Multiply by 10 and divide by 2.
Multiply by 6: Sometimes multiplying by 3 and then 2 is easy.
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 and add 10 times original number.
Multiply by 14: Multiply by 7 and then multiply by 2
Multiply by 15: Multiply by 10 and add 5 times the original number, as above.
Multiply by 16: You can double four times, if you want to. Or you can multiply by 8 and then by 2.
Multiply by 17: Multiply by 7 and add 10 times original number.
Multiply by 18: Multiply by 20 and subtract twice the original number (which is obvious from the first step).
Multiply by 19: Multiply by 20 and subtract the original number.
Multiply by 24: Multiply by 8 and then multiply by 3.
Multiply by 27: Multiply by 30 and subtract 3 times the original number (which is obvious from the first step).
Multiply by 45: Multiply by 50 and subtract 5 times the original number (which is obvious from the first step).
Multiply by 90: Multiply by 9 (as above) and put a zero on the right.
Multiply by 98: Multiply by 100 and subtract twice the original number.
Multiply by 99: Multiply by 100 and subtract the original number.
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If only some of us had gotten this tricks while in secondary school, who knows..........we all could have had A1 mathematics in waec.
-checkout TOP 15 REASONS WHY STUDENTS FAIL www.studentcosmos.com/reasons-why-students-fail-exam

Nice one

:

Wow! Thank you for sharing, page saved I wish Nairaland posts can always be like this but then, variety is the spice of life

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op I didn't just enjoy this, I was also blessed by it.

Nice one

1cor2v9:
op I didn't just enjoy this, I was also blessed by it.

I'm happy you did enjoy it.

now I can go back and repeat secondary school!

h,,

he Be like say I get one math course this semester this would be so useful thanks op

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These are things one should be able to reason out by yourself.

I remember sometime in Jss1 when i somehow noticed that squares of numbers follow a pattern

1, 4, 9, 16, 25, 36.. starting from 1, you just keep adding successive odd numbers, 3, 5, 7, 9, 11, etc to keep getting the next square..

i kept thinking of a way i cud make a little formular out of it till i discovered that i just needed to add the present number to the next number and add it to the square

so for example i need the square of 31 and i know the square of 30(900)..i just add 900 to the present number (30) and then add the next number (31) to get 961..

then i optimized it more the difference between the numbers is 1, and then i knew that last one had to come from that..

finally i tried it with a difference of 2

32 * 32 = ((30 * 30) + 30 + 31) + 31 + 32 = 1024 = 90 + (4 * 30) + 4

i eventualy settled for the square of the number you know plus two times the number you know times the difference from the next number then add the square of the difference


twas later when i started doing factorzation that i realised what i did wasnt magic but actually exlainable

32 * 32 = (30 + 2)(30 + 2) = 900 + 60 + 60 + 4

joycesims:
now I can go back and repeat secondary school!

lols. Very funny

okhiai1:
he Be like say I get one math course this semester this would be so useful thanks op

lols. No P. U re welcome

yorex2011:
These are things one should be able to reason out by yourself.

I remember sometime in Jss1 when i somehow noticed that squares of numbers follow a pattern

1, 4, 9, 16, 25, 36.. starting from 1, you just keep adding successive odd numbers, 3, 5, 7, 9, 11, etc to keep getting the next square..

i kept thinking of a way i cud make a little formular out of it till i discovered that i just needed to add the present number to the next number and add it to the square

so for example i need the square of 31 and i know the square of 30(900)..i just add 900 to the present number (30) and then add the next number (31) to get 961..

then i optimized it more the difference between the numbers is 1, and then i knew that last one had to come from that..

finally i tried it with a difference of 2

32 * 32 = ((30 * 30) + 30 + 31) + 31 + 32 = 1024 = 90 + (4 * 30) + 4

i eventualy settled for the square of the number you know plus two times the number you know times the difference from the next number then add the square of the difference


twas later when i started doing factorzation that i realised what i did wasnt magic but actually exlainable

32 * 32 = (30 + 2)(30 + 2) = 900 + 60 + 60 + 4

you must be very good at maths then. Good one tho.

mathe