Rakib studies with the help of flash cards. He has a set of 30 flash cards out of which 17 cards are white and rest are grey. 4 white and 5 grey cards are marked ENGLISH. Find the possibility of choosing a grey card or an ''ENGLISH'' Card randomly from the set.

We know,
Probability = what we want/Total
Or = add; AND = multiply

We want a grey card OR ENGLISH card
There are 30 - 17 = 13 grey cards
There are 4 + 5 = 9 ENGLISH cards
Total cards = 30
Also, 5 grey cards are ENGLISH cards.

So Probability = 13/30 + 9/30 - 5/30 = (13 + 9 - 5)/30
= 17/30 [This subtraction is needed a grey card gets counted twice - once in 13 grey cards and once again in 9 ENGLISH cards.]