π’1. Square of a 2-digit number ending in 5
If a number ends in 5, you can square it like this :
- Formula – (x5)2 = x*(x+1) and add 25
- Example – (75)2 = 7*8 = 5625
β2. Multiple number near 100
- Trick for number like 98*97 :
(100-a)(100-b) = 10000-100 (a+b) + ab
- Example : 98*97 = 100-2, 100-3
β‘οΈ10000-100(5)+6 = 9506
π§3. Area of Triangle using Heroe’s Formula
- Calculate semi-perimeter : S = a+b+c/2
- Apply :
Area = βs(s-a)(s-b)(s-c)
π Memorize the steps as S-Area formula : SSABBC = s, s-a , s-b , s-c
π4. Divisibility Tricks
- By 3 : Sum of digits divisible by 3
- By 4 : Last 2 digits divisible by 4
- By 11 : Alternating digits sun difference divisible by 11
π’5. a2 – b2 = (a-b)(a+b)
Use it to solve quickly :
- Example :
1042 – 962 = (104-96)(104+96) = 8*200 = 1600