hello friends

 

see firstly in the question nos. should actually be written like  {1,2,3......50}

 

now the soln. is as follows

first case if 40 is max. no. of selections = 39C2

second case if 10 is min.  no. of selections is 40C2

now the question says either 10 is min. or 40 is max. therefore we now have to subtract the AND conditions.

for that assume two out of three nos. are 10 & 40

then the selections become and selections are 11,12,13,14......... 39 because in these cases 40 will become the max. AND 10 will become the min.

therefore total AND cases are 29

 

The error made by joyfrancis was that when he excluded 10 in his firsr case he ignored the selections such as (40,10,1),(40,10,2)