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junior college 2 | H3 Maths
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junior college 2 chevron_right H3 Maths chevron_right Singapore

May i know why am i wrong?

Date Posted: 5 days ago
Views: 22
5 days ago
4/52 + 12/52 = 4/13
Out of 13 spades, only 12 spades will not have 7. The question is asking for spades OR a 7.
3 days ago
Because, in doing 4/52 + 13/52, you were actually double counting the 7 of spades.

We need either a spade or a 7. As long as either condition is satisfied, we can consider that card.

7 ♥, 7♦,7♣ satisfy the second condition.

2,3,4,5,6,8,9,10,J,Q,K,A ♠ satisfy the first condition.

7 ♠ satisfies both. But you must be careful not to double count it since there is only 1 of it.

So the answer is 16/52 = 4/13

If the question asked for 7 only, then B (4/52 = 1/13) would be the answer.

If the question asked for both 7 and a spade, then A (1/52) is correct.