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How many three digit numbers can these numbers make up
There are 10 numbers from 0 to 9
The first one can't be zero, so there are only nine possibilities
The second digit can be 0, deducting the number already used in the first place, so there are still nine possibilities
The third is eight possibilities
The formula is 9 × 9 × 8 = 648 possibilities
How many problems can be solved by using four numbers 0, 1, 2, 3 to form a four digit number without repetition
Using mathematical arrangement method:
The thousand digits can only be expressed as one of 1, 2 and 3, which is C31 = 3;
The hundreds, tens and pieces can be arranged arbitrarily with the remaining three numbers, which is A33 = 6;
In conclusion: C31 * A33 = 3 * 6 = 18
From 0 to 9, ten digits form an addition formula, that is, three digits plus three digits equals four digits without repetition,
There are 96 formulas
246+789=1035,249+786=1035,264+789=1053,269+784=1053,284+769=1053
286+749=1035,289+746=1035,289+764=1053,324+765=1089,325+764=1089
342+756=1098,346+752=1098,347+859=1206,349+857=1206,352+746=1098
356+742=1098,357+849=1206,359+847=1206,364+725=1089,365+724=1089
423+675=1098,425+673=1098,426+879=1305,429+876=1305,432+657=1089
437+589=1026,437+652=1089,439+587=1026,452+637=1089,457+632=1089
473+589=1062,473+625=1098,475+623=1098,476+829=1305,479+583=1062
479+826=1305,483+579=1062,487+539=1026,489+537=1026,489+573=1062
537+489=1026,539+487=1026,573+489=1062,579+483=1062,583+479=1062
587+439=1026,589+437=1026,589+473=1062,623+475=1098,624+879=1503
625+473=1098,629+874=1503,632+457=1089,637+452=1089,652+437=1089
657+432=1089,673+425=1098,674+829=1503,675+423=1098,679+824=1503
724+365=1089,725+364=1089,742+356=1098,743+859=1602,746+289=1035
746+352=1098,749+286=1035,749+853=1602,752+346=1098,753+849=1602
756+342=1098,759+843=1602,764+289=1053,764+325=1089,765+324=1089
769+284=1053,784+269=1053,786+249=1035,789+246=1035,789+264=1053
824+679=1503,826+479=1305,829+476=1305,829+674=1503,843+759=1602
847+359=1206,849+357=1206,849+753=1602,853+749=1602,857+349=1206
859+347=1206,859+743=1602,874+629=1503,876+429=1305,879+426=1305
879+624=1503
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