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Base Method This
is very suitable when numbers are close to a base like 10, 100, 1000 or so
on. Let's take an example: 12 X 14. 10 would the most suitable base. In the current example, the surplus numbers are +2 and +4. If 8x7 were to be performed and base of 10 were chosen, then -2 and -3 would have been the deficit numbers. Try the following numbers (a) 13 X 16 (b) 16 X 18 (c) 18 X 19 (d) 22 X 24 Once you get comfortable, do not use any paper or pen. 27 X 28 322 #9; #9; 23 X 18 46 X 48 5255 582 53 X 57 622 382 42 X 46 #9; #9; 9698 92 X 93 99
X 99 #9; #9; 102 X 105
98 X 107 112X113
1082
123 X 127 USING
OTHER BASES Multiply 32 by 25. Most of the students would take 30 as the base. The method is correct but nonetheless lengthier. Better technique is to understand that 25 is same as one-fourth. Therefore, one-fourth of 32 is 8 and hence the answer is 800. An application of Base Method to learn multiplications of the type 3238, where unit's digit summation is 10 and digits other than unit's digit are same in both the numbers. In the above example, 2 + 8 = 10 and 3 in 32 is same as 3 in 38. Therefore method can be applied. The method is simple to apply. The group of digits other than unit's digit, in this case 3, is multiplied by the number next to itself. Therefore, 3 is multiplied by 4 to obtain 12, which will form the left part of the answer. The unit's digits are multiplied to obtain 16 (in this case), which will form the right part of the answer. Therefore, the answer is 1216. Try these now 53 X 57 91 X 99 106 X 104 123 X 127 The rule for squares of numbers ending with 5. e.g., 652. This is same as 65 X 65 and since this multiplication satisfies the criteria that unit's digit summation is 10 and rest of the numbers are same, we can apply the method. Therefore, the answer is 42 / 25 = 4225. Try these: 352
952
1252
2052
Find (10004)3 Step (I) : Base is 10000. Provide three spaces in the answer.The base contains 4 zeros. Hence, the second and third space must contain exactly 4 digits. 1 0 0 0 4 = —/ —/ — Step (II) : The surplus is (+4). If surplus is written as 'a', perform the operation '3a' and add to the base 10000 to get 10012. Put this in the 1st space.
1 0 0 0 4 = 1 0 0 1 2 /—/— Step (III) : The new surplus is (+12). Multiply the new surplus by the old surplus, i.e. (+4)(+12) = (+48). According to the rule written in the step (I), 48 is written as 0048. 1 0 0 0 4 = 1 0 0 1 2 / 0 0 4 8 /— Step (IV) : The last space will be filled by the cube of the old surplus (+4). Therefore, 43 = 64, which is written as 0064. 1 0 0 0 4 = 1 0 0 1 2 / 0 0 4 8 / 0 0 6 4 Therefore, the answer is 1001200480064. Find (998)3 Step (I) : Base = 1000. Hence, exactly 3 digits must be there in the 2nd and 3rd space.The deficit = (+2) 9 9 8 = —/—/— Step (II) : Multiply the deficit by 3 and subtract (because this is the case of deficit) from the base. 9 9 8 = 9 9 4 /—/— Step (III) : (old deficit) x (new deficit) = 2 x 6 = 12 9 9 8 = 9 9 4 / 0 1 2 /— Step (IV) : The cube of the old deficit = 8. Since it is the case of deficit, -8 should be written. All that you need to do to write the negative number in the third space is to find the complement of the number, in this case 8. But since the third space must have exactly 3 digits, the complement of 008 must be calculated. The complement of 008 is 992. Don't forget to reduce the last digit of the second space number by 1 9 9 8 = 9 9 4 / 0 1 2 / 9 9 2 - 1 ———————————— 9 9 4 / 0 1 1 / 9 9 2 Therefore, the answer is 994011992 As an exercise, try the following : 999943 = 9 9 9 8 2 / 0 0 1 0 8 / 0 0 2 1 6 = 99982/00107/99784 100053 = 1 0 0 1 5 / 0 0 7 5 / 0 1 2 5 = 10015/0075/0125 1000253 = 1 0 0 0 7 5 / 0 1 8 7 5 / 1 5 6 2 5 = 100075/01875/15625 99999883 = 9 9 9 9 9 6 4 / 0 0 0 0 4 3 2 / 0 0 0 1 7 2 8 = 9999964/0000431/9998272
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