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Slide 1Welcome to the World of MATHEMA-TRICKSMinhas KamalToday we will learn some cool math tricks.So that, we can use more our brain and less our calculator.1Square a two digit number ending in 5For example: 152, 452, 852 2Square a two digit number ending in 5Lets consider the number 35.1. We take the first digit and multiply it with its nextnumber.3 5 3 * 4 = 122. Then simply put 25 after it.1 2 2 5So, 352 = 12253Square a two digit number ending in 5Here is another example:Step-1:9 5 9 * 10 = 90Setp-2:9 0 2 5So, 952 = 90254Multiply any number by 4Simply double the number two times.5Multiply any number by 4Take the number 6363*4 = 63*(2*2) = (63*2)*2 = 126*2 = 252Lets try another number 753double of 753 = 1506double of 1506 = 3012So, 753 * 4 = 30126Multiply any number by 5Simply half the number &multiply it by 10.7Multiply any number by 5Take the number 8686*5 = 86*(10/2) = (86/2)*10 = 43*10 = 430Lets try another number 495half of 495 = 247.5247.5 * 10 = 2475So, 495 * 4 = 24758Multiply any number by 15Multiplication by 10 + Multiplication by 5.9Multiply any number by 15Take the number 8484*10 = 84084*5 = (84/2)*10 = 42*10 = 42084*15 = 840 + 420 = 1260Lets try another number 495495*15 = 495*10 + 495*5 = 4950 + (495/2) * 10 = 4950 + 2475 = 742510Multiply any number by 11xyzxy + zzx + yxyz * 11=11Multiply any number by 11Take the number 263Lets try another number 4852632938263 * 11=4855353263 * 11=1112Multiply two numbers between 10 and 20For example: 15*17, 19*13 13Multiply two numbers between 10 and 20Lets consider the number 12*14.1. Add the first number with the other numberssecond digit.1 2 + 1 41 62. Place a 0(zero) after it.1 6 1 6 014Multiply two numbers between 10 and 203. Multiply the second digits of the two numbers.1 4 * 1 2 84. Add this number with the step-2 result.1 6 0 + 81 6 8So, 12*14 = 16815Multiply two numbers between 10 and 20Here is another example: 17*13 Step-1:17 + 3 = 20 Setp-2:20 200 Step-3:7 * 3 = 21 Step-4:200 + 21 = 221 So, 17*13 = 22116Divisibility CheckFor example: is 7403 is divisible by 11 ?17Divisibility Check (for 2, 3)A number is divisible by 2 if its last digit is 0, 2, 4, 6 or 8. For example: 12, 5394, 993120. A number is divisible by 3 if sum of its digits is divisible by 3. For example: 72 is divisible by 3 as 7+2=9 which is divisible by 3.Another example: 57381, 5+7+3+8+1=24; 24 is divisible by 3. So 57381 is also divisible by 3.18Divisibility Check (for 5, 7)A number is divisible by 5 if its last digit is 0 or 5. For example: 100, 3795, 698170. For 7, separate & double the last digit of the number. Then subtract it from the rest. Take: 91. 919 19 - (1*2) 7 Now, if the number is 0 or divisible by 7, then the original number is also divisible by 7.19Divisibility Check (for 7)If the number is big then continue the process as many time as needed. Lets take 3752.3752 375 2*2 371 37 1*2 35 Now, 35 is divisible by 7. So, 3752 is also divisible by 7.You may have gone even further, 35 3 - 5*2 -7 ; which is also divisible by 7.20Divisibility Check (for 11)For 11, add and subtract digits in an alternative pattern (like- 1st digit - 2nd digit + 3rd digit ).Take: 85258 - 5 + 2 - 5 = 0So, it is divisible by 11. Take: 3927553 - 9 + 2 - 7 + 5 - 5 = -11Also divisible by 11 21Divisibility Check (for 13)For 13, add 4 times of the last digit to the rest of the number. Take: 351 351 35+1*4 39 It is divisible by 13.Lets try another: 754 754 75 + 4*4 75 + 16 91 9+1*4 13 So, you know.22So we have leant a lot of math tricks today.Practice to make them perfect for you.23There is one math trick only for YOU!24Lets see if you can do it right!25Add these numbers one after another- 1000 2026Add these numbers one after another- 1000 201000 3026Add these numbers one after another- 1000 201000 301000 4026Add these numbers one after another- 1000 201000 301000 401000 1026Add these numbers one after another- 1000 201000 301000 401000 105000 ???26Add these numbers one after another- 1000 201000 301000 401000 105000 ???If your answer is 5000, then you are among the most who mistook. The actual answer is 4100. Count again and see if you get it right this time. 26www.facebook.com/think.stupid.eduwww.youtube.com/c/thinkstupidedu