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# Tips & Tricks in mathematics

4 Apr 2015
1 sur 12
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### Tips & Tricks in mathematics

1. Introduction In mathematics tricks are important to do calculation faster and easier. In these slides we will show you some tricks for fast and easy calculation.
2. Multiplying by 4 This trick is very simple and yet logical. To multiply any number by 4, just multiply it by 2 and then double the answer. The basic concept of this trick is that you can solve a multiplication problem by multiplying by its factors. Let’s assume the number is 25. Then: 25 x 4 25 x 2 = 50 50 x 2 = 100 25 x 4 = 100 This trick is based on a very simple fact: 2 x 2 = 4
3. Multiplication by 5 It's often more convenient instead of multiplying by 5 to multiply first by 10 and then divide by 2. For example, 137×5 = 1370/2 = 685.
4. Multiplying by 12 12 X 7 The first thing is to always multiply the 1 of the twelve by the number we are multiplying by, in this case 7. So 1 X 7 = 7. Multiply this 7 by 10 giving 70. (Why? We are working with BASES here.) Bases are the fundamentals to easy calculations for all multiplication tables. Now multiply the 7 by the 2 of twelve giving 14. Add this to 70 giving 84. Therefore 7 X 12 = 84
5. Multiplication of 2 Numbers Step 1: Let us consider multiplying any two digit numbers, for example 23 x 24. Step 2: Choose the unit digit of both the numerals and deduct it from the given numerals. 23 - 3 = 20 24 - 4 = 20 Step 3: Now, select any one number (24) and add it with unit digit of another number(3) 24 + 3 = 27 Step 4: Then, multiply the result obtained in step 2 and step 3. 27 x 20 = 540 Step 5: Multiply the unit digit values. 4 x 3 = 12 Step 6: Finally, add values obtained from step 3 and step 4. 540 + 12 = 552 23 x 24 = 552
6. Multiplication of 3 Numbers Step 1: Let us consider multiplication of three digit numbers 208 x 206. Step 2: Now, deduct the last digit from the respective numerals. 208 - 8 = 200 206 - 6 = 200 Step 3: Pick any one number and add it with the unit digit of another number. 208 + 6 = 214 Step 4: Now, multiply the result obtained in step 1 and step 2. 214 * 200 = 42800 Step 5: Then, multiply the unit digits of the given numbers. 8 * 6 = 48 Step 6: Add the values obtained in step 4 and step 5. 42800 + 48 = 42848 208 x 206 = 42848
7. To check divisibility of a number 2- A number is divisible by 2 if it is even. 3- A number is divisible by 3 if the sum of the digits is a multiple of 3. Eg.)12-1+2=3 4-A number is divisible to 4 if the last two digits of the number are divisible by 4. 5-A number is divisible by 5 if the last digit is 5 or 0. 6-A number is divisible by 6 if the number is divisible by 2 and 3. 7-A number is divisible by 7 if you double the last digit and subtract it from the rest of the number and the answer is: 0, or divisible by 7. 8-The last three digits are divisible by 8. 9-The sum of the digits is divisible by 9. 10-The number ends in 0. 11-If you sum every second digit and then subtract all other digits and the answer is:0, or divisible by 11. 12-The number is divisible by both 3 and 4.
8. Squaring of numbers ending with 5 65x65=4225 Multiply the previous number 6 to one more than itself 7. Then write 25.
9. Squaring two digit numbers Say, you want a square of 13. Do this: add 3 (the last digit) to 13 (the number to be squared) to get 16 = 13 + 3. Square the last digit: 3² = 9. Append the result to the sum: 169.
10. Distributive Property The Distributive Property is an algebra property which is used to multiply a single term and two or more terms inside a set of parentheses. Eg.) 103+101=100(3+1)
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