Concept of math for children

1. 1
HARSHIT GUPTA
B.C.A. –FIRST YEAR
SECOND SEMESTER
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2. 2
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3. Lets learn
multiplication of 2 digit
numbers.
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4. Suppose we have to
multiply 97 X 98 :
We should take 100
as the base of our
calculation because
it is the nearest
unity to the
numbers to be
multiplied.
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5. For
Example
97-02
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6. Now lets learn
multiplication above the
base.
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7. Suppose we have to
multiply 12 X 14 :
We should take 10
as the base of our
calculation because
it is the nearest
unity to the
numbers to be
multiplied.
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8. For
Example
CLICK HERE TO GO TO THE MAP
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9. 9
D
Here we come to
know about
Digital root

10. Definition
• Digital root of a number is the single
digit obtained by repeatedly summing all
the digits of a number.
• Example:
• Digital root of 2357 = 8
because (2 + 3 + 5 + 7 = 17) and (1 + 7 = 8)
• Digital root of 89149 = 4
because (8 + 9 + 1 + 4 + 9 = 31) and (3 + 1 = 4)
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11. Some facts we already
know
• A number is divisible by 3 if its
digital root is divisible by 3 (that is, it
is 0, 3, 6, or 9).
• 1236 is divisible by 3 because 3 is divisible
by 3.
• Note (1+2+3+6 = 12) and (1+2 = 3).
• Recall: 1x(999+1) + 2x(99+1) + 3x(9+1) + 6
• A number is divisible by 9 if its
digital root is divisible by 9 (that is, it
is 0 or 9). 11

12. (cont’d)
• The digital root of a number is the
remainder obtained by dividing it by 9.
• 1236 divided by 9 = … R 3
• Recall: 1x(999+1) + 2x(99+1) + 3x(9+1) + 6
• Note that 9 is treated similar to 0.
• 36 divided by 9 = … R 0
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13. Properties of digital roots
• Digital root of a square is 1, 4, 7, or 9
• Digital root of a perfect cube is 1, 8 or 9
• Digital root of a prime number (except
3) is 1, 2, 4, 5, 7, or 8
• Digital root of a power of 2 is 1, 2, 4, 5,
7, or 8
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14. Justification for digital
roots of a prime number
• Recall that digital root of 0, 3, 6, or 9
implies it is divisible by 3.
• The digital root of 1, 2, 4, 5, 7, and 8 are
realizable by the prime numbers 19, 2
(11), 13, 5 (23), 7 (43), and 8 (17),
respectively.
– This is a necessary (but not sufficient)
condition for a number to be prime.
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Product of both digital
root then find
Digital root
Digital root of
answer
Digital root of
first number

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7*8=>56=5+6
=>11=>1+1=>2
25
2+5
=7
26
=> 2+6
=>8
25*26=650=>6+5+0
=>11=>1+1=>2

17. 17
Last Digit of Perfect
Square Root number
Last digit of root
1 1 Or 9
4 2 Or 8
5 5
6 4 Or 6
9 3 Or 7
Find the Square root of 5041
now 5041 1
Then √50>=7
Then we have to option 71 or 79
Check than we say √5041=71 9
Square
Root ?

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