binomial distribution

here the problem is broken by pages so i added two images.There it has chosen 12c8 .we should have chosen 12c12,shouldn't we?

bhuvaneshnick said:

here the problem is broken by pages so i added two images.There it has chosen 12c8 .we should have chosen 12c12,shouldn't we?
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Why are you saying 12 instead of 8? Is it because they said 8 heads and 4 tails? That is, if they had just said exactly 8 heads would you think that they are correct? If you tossed 12 coins and got 8 heads does it not follow that you did get 4 tails? Tell us why you think the 8 should be a 12 and we can better help you.

yes if they said just 8 heads i have assumed its right ,here it is also given 4 tails but in formula we have not show any interest on 4 tails