Each of the integers from 0 to 9, inclusive, is written on a seperate slip of blank paper and the ten slips are dropped into hat. If the slips are then drawn one at a time without replacement, how many must be drawn to ensure that the numbers on two of the slips drawn will have a sum of 10?
pls explain simply to me
The numbers that will add up to 10 are
to be sure we need 5,0, 4 of the above numbers + at-least 1 more
because we can have 5,0,9,8,7,6 which will not guarantee a sum of 10 for any 2 numbers but one more digit can guarantee the sum to be 10. i.e. 5,0,9,8,7,6 and any of (1,2,3,4) hence we need at-lease 7 numbers.