Quicker Maths

## Quick Multiplication by 5

Posted on May 21, 2012

Tricks for fast calculation by 5

It is a simple trick which is very intuitive and easy to understand. Many QuickerMaths.com followers might find it very simple. However, there are many who will enjoy this simple yet readily usable trick to multiply any number by five.

1. Multiplying 5 times an even number: halve the number you are multiplying by and place a zero after the number.

Example:

i. 5 * 136, half of 136 is 68, add a zero for an answer of 680.

ii. 5 * 874, half of 874 is 437; add a zero for an answer of 4370.

2. Multiplying 5 times an odd number: subtract one from the number you are multiplying, then halve that number and place a 5 after the resulting number.

Example:

i. 343 * 5 =

Subtract 1 from 343 and half the result = 171. Right hand side will always by 5. Hence the answer is 1715

or, (343-1)/2         |          5        =       1715 .

Let me know if you enjoyed this post.

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#### Posted by Vineet Patawari

1. I think there’s a alternative to the trick of multiplying by 5.

132/5
1/2 of 132 =66 and multiply by 10 which gives 660

133/5
1/2 of 133=66.5 and multiply by 10 which gives 665

Hence there is no need to remember the trick for even and odd numbers separately. Hope you agree with it . @vineet Patawari Sir

2. can you please send me some more tricks about the multiplication of any two numbers

3. Ok well let me submit something.
I hope you will like it vineet.
In a triangle.
we know the relation ship between sides and angles with trignometry.
but how can we find out angles if we know the sides in a simple method?
use ‘&’ as the proportionality symbol.
in a triangle ABC the side opposite to angleA is BC , side opposite to angleC is AB etc.
so as the side AB increases then angleC definitely increases. right?
so
AngleA & BC (& —> means directly proportional to)
AngleB & AC
AngleC & AB
Let ‘P’ be a constant.
AngleA = P(BC) —–> 1
AngleB = P(AC) ——>2
AngleC = P(AB) ——>3
AngleA+AngleB+AngleC = P(BC+AC+AB)
But AngleA+AngleB+AngleC = 180
therefore, 180= P(BC+AC+AB)
=> P= 180/(BC+AC+AB)
from formula if we know the 3 sides of a triangle we can find the constant ‘P’.
and to get an angle.
AngleA = P(BC)
so multiply P with a side opposite to the angle to get that angle.
here is an Example sum.
2,6,10 are the 3 sides of a triangle. Find out all their angles.
From my formula above, P = 180/(AB+BC+CA)
AB+BC+CA = 2+6+10 = 18
=> P=180/18
=10
therefore P=10 degrees per unit distance.
that means if there is an increase of 1 unit distance then the angle opposite to that side increases by 10 degrees.
AngleA = 10(BC) = 10(2) = 20 degrees
AngleB = 10(CA) = 10(6) = 60 degrees
AngleC = 10(AB) = 10(10)=100 Degrees
Therefore the angles are found.
Note: This formula can be used for any type of triangle and this formula is 100% usable and proved.
Note:The value of P is different for different triangles. So we always have to find P before finding angles.
Feel Free to use it and please publish this on this site.

• if sides are 4,3,5 …den according to ur formula p= 180/12 = 15..
angles are 4*15=60
3*15=45
5*15=75
but in real 4,3,5 is a right angle tringle..(4^2 + 3^2 = 5^2)..

4. sir plz provide me the answer of this question
Q–)Statmnts– Some boats are camels, no boats is a soil, all camels are tiles
conc–I) No soil is a tile
2) some boats are tiles
3-) some camels are soils
4-) Some camels are not soils
sir, its answer is 2 & 4 or 1 &2 . plz help me sir

5. nce 1

6. Good

7. Hi, Excellent. Nice job. Continue.

8. Good and easy one……….

9. GREAT, and very easy

10. Cool math trick. I will send this to my bro who is taking a bunch of math classes now.

11. I guess the one I have at

http://www.mbaguys.net/blogs/shabbir/mentally-multiply-5-50-500-5000-143/

Can also work. Its more general