Condition : This trick is used when we multiply quickly two similar numbers with unit digit adding up to 10.( All digits are similar other then unit digit)
Example. 57×53 , 91×99 ,114×116 , 102×108
step 1→ 10×(10+1) / 7×3
step 2→ 10×11 / 21
step 3→ 110 / 21
Answer is 11021
step 1→ 11×(11+1) / 9×1
step 2→ 11×12 / 09 (because 2nd part of 2 digits)
step 3→ 132 / 09
Answer is 13209
step 1→ 15×(15+1) / 2×8
step 2→ 15×16 / 16
step 3→ 240 / 16
Answer is 24016
step 1→ 6×(6+1) / 4×6
step 2→ 6×7 / 24
step 3→ 42 / 24
Answer is 4224
Note: 2nd part have always 2 digits.
Illustration 1 :
107×103
Solution:
1st part / 2nd part (2 digits)
107×103
Solution:
1st part / 2nd part (2 digits)
step 1→ 10×(10+1) / 7×3
step 2→ 10×11 / 21
step 3→ 110 / 21
Answer is 11021
Illustration 2 :
119×111
Solution:
1st part / 2nd part (2 digits)
119×111
Solution:
1st part / 2nd part (2 digits)
step 1→ 11×(11+1) / 9×1
step 2→ 11×12 / 09 (because 2nd part of 2 digits)
step 3→ 132 / 09
Answer is 13209
Illustration 3 :
152×158
Solution:
1st part / 2nd part (2 digits)
152×158
Solution:
1st part / 2nd part (2 digits)
step 1→ 15×(15+1) / 2×8
step 2→ 15×16 / 16
step 3→ 240 / 16
Answer is 24016
Illustration 4 :
64×66
Solution:
1st part / 2nd part (2 digits)
64×66
Solution:
1st part / 2nd part (2 digits)
step 1→ 6×(6+1) / 4×6
step 2→ 6×7 / 24
step 3→ 42 / 24
Answer is 4224
Note: 2nd part have always 2 digits.
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