Help me with this simple question please

Question

a pencil case contains some blue, yellow, red and green eraser

each student is to pick two eraser of different colour

how many students will there be before two of them pick the eraser of the same colour combination?

Answer 1

b,r,y and g

6 possible combinations

b&r

b&y

b&g

r&y

r&g

y&g

the 7th student will with 100% probability choose a combo that is the same as a prior student's combination

the 1st student could do it, 2nd, 3rd, 4th, 5th or 6th could do it

will odds increasing, then reaching 100% chance with the 7th student