Multiplication Tricks - Find solution within 20 seconds

When sum of ten's digit is 10 and unit digit is same

46 × 66
= ( 4×6 ) +6 / 6×6
= 24 + ⁶/36
= ³⁰/ 36
Ans = 3036

83 × 23
= ( 8×2 ) +3 / 3×3
= ¹⁹/09
Ans = 1909

92 × 12
= ( 9×1 ) + 2/2 × 2
= ¹¹/04
Ans = 1104

When unit digit is 5 in both the numbers and difference between both number is 10.

75 × 65

=  6 × ( 7+1 ) / 75
=  ⁴⁸/75
Ans = 4875

45 × 35
= 3 × ( 4+1 )/75
= 15 /75
Ans = 1575

105 × 95
= 9 × ( 10+1 ) / 75
= 99/75
Ans = 9975

Find the unit digit  of 147¹²⁸ * 138¹⁴⁸ ?

Updated on 12th October 2015

Multiply by 11,111,1111....so on

Ques 1. 111111111 ✘ 111111111 = ?

Sol:
No of digits in multiplier = 9
Write in ascending order from left side like this:
987654321
and now 9-1=8
write it in descending order just after it
12345678
now you will get like this:
12345678987654321
hence
111111111✘111111111 = 12345678987654321

Ques 2. 1111111111 ✘ 1111111111 = ?
Sol:
No of digits in multiplier =10
Write in ascending order from left side like this:
10 9 8 7 6 5 4 3 2 1
and now 10-1=9
write it in descending order just after it
1 2 3 4 5 6 7 8 9
and after it just add the carry
1 2 3 4 5 6 7 8/ 9/ 10 9 8 7 6 5 4 3 2 1
                  8+1/   9+1 / 0
1 2 3 4 5 6 7 9 0 0 9 8 7 6 5 4 3 2 1
now you will get like this:
1234567900987654321
hence
1111111111✘1111111111 = 1234567900987654321

Ques 3. 1111111✘2222222 = ?
Sol:
No of digit in the multiplier is 7 then let n=7;
Now Just multiply the digit 2 from 1 to 7 time & arrange them from extreme left to right in ascending order,you will get like this:
14 12 10 8 6 4 2
and now just subtract one from n.like this n=7,so n-1=6.
Multiply the digit 2 from 1 to 6 time & arrange them from just right after it,you will get like this:
2 4 6 8 10 12
Now placing both outcome like this & add the carry
2 4 6 8 10 12 14 12 10 8 6 4 2
        8+1/0+1/2+1/4+1/2+1
You will get the answer:
2 4 6 9 1 3 5 3 0 8 6 4 2

Ques 4. 1111111✘5555555 = ?
Sol:
No of digit = 7
Now Just multiply the digit 5 from 1 to 7 time & arrange them from extreme left to right in ascending order,you will get like this:
35 30 25 20 15 10 5
Just right after it perform same action but in descending order & till 6 times only.like this:
5 10 15 20 25 30
Now placing together ,just add the carry
5 10 15 20 25 30 35 30 25 20 15 10 5
6 1 7 2 8 3 8 2 7 1 6 0 5
1111111✘5555555=6172838271605

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