There are 10 digital cards, at least a few cards out, in order to ensure that there are both odd and even numbers? Explain the principle of mathematics

There are 10 digital cards, at least a few cards out, in order to ensure that there are both odd and even numbers? Explain the principle of mathematics

There are 5 odd cards and 5 even cards for each of the 10 cards, so you should draw at least:
5x1 + 1 = 6 sheets
There are even numbers and odd numbers!

How many cards should be drawn out of one to five digital cards to ensure that the cards drawn have both odd and even numbers? Why

Odd number: 3
Even number: 2
There are both odd and even numbers: 3 + 1 = 4
A: draw at least 4 cards to ensure that the cards drawn are odd and even

Given the 12 numbers 1,2,3,. 11 and 12, after adding a negative sign before some of them, make the sum of these 12 numbers 0, please write an expression
At least one

1-2-3+4+5-6-7+8+9-10-11+12=0