2014 A-level H2 Mathematics (9740) Paper 2 Question 10 Suggested Solutions

All solutions here are SUGGESTED. Mr. Teng will hold no liability for any errors. Comments are entirely personal opinions.

(i)
(a) Required Probability $= (0.1)(0.2)(0.1) = 0.002$

(b) Required Probability
$= 1 - \mathrm{P(no~stars)}$
$= 1 - (0.9)(0.8)(0.9) = 0.352$

(c)
$\mathrm{P}(\times \times +) + \mathrm{P}(\times + \times) + \mathrm{P}(+ \times \times )$
$= (0.3)(0.1)(0.2) + (0.3)(0.3)(0.4) + (0.4)(0.1)(0.4)$
$= 0.058$

(ii)
$\mathrm{P}(exactly~ 1 ~star)$
$= (0.1)(0.8)(0.9) + (0.2)(0.9)(0.9) + (0.1)(0.9)(0.8)$
$=0.306$

$\mathrm{P}(+,\circ~|~ exactly ~1 ~star)$

$=\frac{\mathrm{P}(+,\circ, \star)}{\mathrm{P}(exactly 1 \star)}$

$=\frac{(0.4)(0.4)(0.1)+(0.4)(0.2)(0.3)+(0.2)(0.3)(0.1)+(0.2)(0.2)(0.2)+(0.1)(0.3)(0.3)+(0.1)(0.4)(0.2)}{0.306}$

$= \frac{71}{306}$

Personal Comments:
This question was a question that a few students of mine was jokingly telling me they see stars here. To be honest, this is not super hard. Just extremely tedious.

A-level H2 Mathematics Paper 2 Probability Statistics Suggested Solution Year 2014

About

KS Teng

KS has been teaching H2/H1 Mathematics and IB mathematics for the more than 10 years. Having taught students from all various Junior Colleges, KS adapts to students' abilities and help them better understand the topics. As someone who loves to teach mathematics and sees it as a truly useful tool in life, KS seeks to enable students to appreciate math. Therefore, his tuition mission is to motivate and cultivate students to be independent and confident thinkers.

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