Quick Multiplication by 5

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.


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.


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 .

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Vineet Patawari

Hi, I'm Vineet Patawari. I fell in love with numbers after being scared of them for quite some time. Now, I'm here to make you feel comfortable with numbers and help you get rid of Math Phobia!

17 thoughts to “Quick Multiplication by 5”

  1. 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?
    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
    Adding 1,2,3 we get……
    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
    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.

  2. 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

      1. @Santhakumar
        from stmnt1+stmnt2 ie some boats are camels +all camels are tiles => some boats are tiles (cncln 2)

        Now stmnt 1 can be converted into ‘some camels are boats ‘+ no boats is a soil(stmnt2) = some camels are not soils(concln 4) {I+E=O}

        SO ANSWER IS 2 & 4.

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