======================================= Left To Right Mental Addition ======================================= This is a description of how to add numbers quickly, accurately, and painlessly using only your brain. To read English you memorized each letter of the alphabet and the sounds they represent. The sounds are joined together from left to right to make words such as d-o-g and c-a-t. We develop the skill to read without having to consciously sound out the letters of every word. Left to right mental addition is similar and anyone can do it! ======================================= Keep it simiple stupid --------------------------------------- The secret to left to right mental addition is having the skill to recognize the sum of two digits. Develop the skill to instantly recognize the sum of two digits as effortlessly as a nickel and a penny. My method of mental addition only requires the digits 0 1 2 3 4 5 6 7 8 9 and nothing more. Do not use words such as "and", ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, twenty, hundred, thousand, etc. which are words that define various numbers consisting of multiple digits. If the sum of two digits is two digits then the first digit will always be a one. Say each digit such as "one oh", "one one", "one two", "three one nine", etc. the same way they do in many oriental languages. Words are used when you want to communicate a number in a fancy way such as "seven hundred and seventeen thousand three hundred and eleven". ======================================= Break down numbers into digits --------------------------------------- This is a kin to adding round numbers such as 300 + 250. Break down numbers into digits and add them column by column from left to right always saying the digits. 321 + 654 break it down --> 321 + 6.. + 5. + 4 say the first number --> 321 three two one add the column --> 6.. --- say the sum --> 921 nine two one add the column --> 5. --- say the sum --> 971 nine seven one add the column --> 4 --- say the sum --> 975 nine seven five 52 + 43 break it down 52 + 4. + 3 progression 52 > 92 > 95 five two > nine two > nine five 96 + 23 break it down 96 + 2. + 3 progression 96 > 116 > 119 nine six > one one six > one one nine ======================================= Carry One --------------------------------------- "Carry" is the task of adding 1 to the previous column. If a column sum is two digits then we remove the first digit, which will always be a 1, and increment the previous column. 25 + 9 say the first number --> 2 5 two five add the column --> 9 --- increment the carry --> 2 14 say the sum --> 3 4 three four 19 + 12 progression 19 > 29 > 31 one nine > two nine > three one 78 + 28 progression 78 > 98 > 106 seven eight > nine eight > one oh six 85 + 36 progression 85 > 115 > 121 eight five > one one five > one two one Pre-increment the column sum as soon as you recognize there is a carry in the next column. 25 + 9 progression 25 > 34 two five > three four 19 + 12 progression 19 > 31 one none > three one 78 + 28 progression 78 > 106 seven eight > one oh six 85 + 36 progression 85 > 121 eight five > one two one ======================================= Make it as simple as possible but not simpler --------------------------------------- Adding more than two numbers such as 123 + 123 + 123 done adding two at a time the same way computers do. 123 + 123 = 246 246 + 123 = 369 Clean up dirty numbers to save brain cells. 3001 + 1999 is easier as 3000 + 2000 2950 + 3465 is easier as 3000 + 3415 Round up any number by making each column add to 9 and the last non zero column add to 10. 43210 <-- to round this up to 50000 6790 <-- make 9's and a 10 ----- 50000 <-- rounded up 1001 12345 111100 1020202 <-- to round up 999 7655 88900 979798 <-- make 9's and a 10 ---- ----- ------ ------- 2000 20000 200000 2000000 <-- rounded up Calculate your change when you pay with cash. 68.53 <-- when you get your bill 31.47 <-- make 9's and a 10 to get your change 100.00 <-- when you pay with cash ======================================= Count in multiples --------------------------------------- Counting in multiples is adding the same digit. By saying the digits you will notice patterns as you add and carry. No points are awarded if you say words like ten eleven twelve instead of "one oh" "one one" "one two". 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 5 10 15 20 25 30 35 40 45 50 55 60 65 70 85 80 85 90 95 100 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102 108 114 120 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105 112 119 126 133 140 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120 128 136 144 152 160 9 18 27 36 45 54 63 72 81 90 99 108 117 126 135 144 153 162 171 180 Advanced counting. 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 11 22 33 44 55 66 77 88 99 110 121 132 143 154 165 176 187 198 209 220 12 24 36 48 60 72 84 96 108 120 132 144 156 168 180 192 204 216 228 240 13 26 39 52 65 78 91 104 117 130 143 156 169 182 195 208 221 234 247 260 14 28 42 56 70 84 98 112 126 140 154 168 182 196 210 224 238 252 266 280 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 272 288 304 320 17 34 51 68 85 102 119 136 153 170 187 204 221 238 255 272 289 306 323 340 18 36 54 72 90 108 126 144 162 180 198 216 234 252 270 288 306 324 342 360 19 38 57 76 95 114 133 152 171 190 209 228 247 266 285 304 323 342 361 380 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 Count in multiples starting with an offset. For example count by 6 with an offset. 0: 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102 108 114 120 1: 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103 109 115 121 2: 8 14 20 26 32 38 44 50 56 62 68 74 80 86 92 98 104 110 116 122 Counting backwards is also a good skill to develop for subtraction. It may be easier than reciting the alphabet backwards. You can practice left to right mental addition here https://www.oetec.com/add o1