Eric Nicholas K's answer to Xiang Ning's Junior College 2 H2 Maths Singapore question.

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Eric Nicholas K
Eric Nicholas K's answer
5997 answers (Tutor Details)
1st
Not 100% sure. My answers are likely wrong.

For part ii, we simply model the binomial distribution by n = 6, p = 0.8 and 1 - p = 0.2, then the general term in the expansion of the binomial formula will be like

(6 r) * 0.2^(6 - r) * 0.8^r

We just sub in integer values of r from 0 to 6 and see the highest one for the most likely integer number of puzzles completed. Of course, adding the probability values for the seven cases must get you 1.
Xiang Ning
Xiang Ning
4 years ago
Actually, part (iv) answer is 0.737
Eric Nicholas K
Eric Nicholas K
4 years ago
I have this checked when I return
Eric Nicholas K
Eric Nicholas K
4 years ago
Oh, the given answer is correct. I lost the translation along the way and misinterpreted “at least 4 correct for the rest of the week” as “exactly 4 correct for the rest of the week”.

In other words, you must do the 5C5 case in my working for part iv in which I only wrote 5C4.

Wait while I update this around 2 am.
Xiang Ning
Xiang Ning
4 years ago
Okay thanks
Eric Nicholas K
Eric Nicholas K
4 years ago
Updated
Xiang Ning
Xiang Ning
4 years ago
Thanks