1 votes 1 votes let S be the set of natural numbers whose digits are chosen from {1,3,5,7} such that no digits are repeated find 1) |S| 2) $\sum (n)$ where n belongs to s first part i know 64 numbers would be there how to approach 2nd part Kaluti asked Jul 27, 2017 Kaluti 323 views answer comment Share Follow See all 0 reply Please log in or register to add a comment.
0 votes 0 votes length 1: 1 or 3 or 5 or 7 $\sum \left ( 1+3+5+7 \right )$=16 length 2: 13,15,17,31,35,37,51,53,57,71,73,75=$\sum \left (13,15,17,31,35,37,51,53,57,71,73,75 \right )$=527 similarly length 3: 10656 length 4: 106656 Tesla! answered Jul 27, 2017 Tesla! comment Share Follow See all 2 Comments See all 2 2 Comments reply Kaluti commented Jul 27, 2017 reply Follow Share we can go for this manual method if set given is small but what if the set given is large then we can not go for this method as we may skip some strings is there any other method here which ensures correct solution in any case 0 votes 0 votes Tesla! commented Jul 27, 2017 reply Follow Share currently i am not able to think of any other method, and to make sure that you don't miss any case use tree method. like fix 1 then 3 branches are possible 3,5,7 now fix 3, then 2 branches are possible 5,7 fix 5 then 7,3 and fix 7 then 5,3 now repeat for other numbers 0 votes 0 votes Please log in or register to add a comment.