Use the addition rule to find the probability of the following event: Obtaining a sum of 6 or doubles (same number on each die) when a pair of dice is rolled once. Express your answer as a decimal rounded to 1 decimal place.

Soluzione

U se t h e a dd i t i o n r u l e t o f in d t h e p ro babi l i t y o f t h e f o ll o w in g e v e n t : O b t ainin g a s u m o f 6 or d o u b l es (s am e n u mb er o n e a c h d i e) w h e n a p ai r o f d i ce i s ro ll e d o n ce . E x p ress yo u r an s w er a s a d ec ima l ro u n d e d t o 1 d ec ima l pl a ce .

Soluzione

\frac{5}{18}

Decimale

0.27777 \dots

Fasi della soluzione

Find the probability of the following event : Obtaining a sum of 6:

\frac{5}{36}

Find the probability of the sum doubles ( same number on each die ) when a pair of dice is rolled once:

\frac{1}{6}

Find the probability of the following event : Obtaining a sum of 6 and the sum doubles ( same number on each die ) when a pair of dice is rolled once:

\frac{1}{36}

Use the Inclusion-Exclusion formula

P (X \lor Y) = P (X) + P (Y) - P (X \land Y)

= \frac{5}{36} + \frac{1}{6} - \frac{1}{36}

\frac{5}{36} + \frac{1}{6} - \frac{1}{36} = \frac{5}{18}

= \frac{5}{18}

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