Hi, can somebody explain this? Also what specific topic is this so I can research it more (I know it's probability but what type) ? thanks

So, we have two possibilities.

The counters can either be both pink or both red.

The probability of one counter being red is 15/20. The probability of the other counter being red, after you have picked one red counter out of the bag, is 14/19 (as there is one less red counter in the bag).

To get the total probability of both counters being red, you do 15/20 * 14/19, which equals 21/38 (when you simplify the fraction).

We do the same for the pink counters. Therefore, we get 5/20 * 4/19, which equals 1/19 (when you simplify the fraction - calculator should do this for you).

To get the total probability of the two counters being the same colour, you must add the two fractions we just worked out:

21/38 + 1/19

You should get: 23/38.

You might not understand why this is the case but I would recommend checking out 'Tree Diagrams' if you want extra information.

Feel free to ask any more questions on this or other topics that you may have. If you read up something that you don't understand on a different website, let me know and I can explain :)