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December 3rd, 2016, 09:28 AM   #1
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"And" and "Or" Probability

Sheila either walks or cycles to school.
The probability that she walks to school is 0.65.

If she walks, the probability that she will be late is 0.4.
If she cycles, the probability that she will be late is 0.1.

Work out the probability that on any one day Sheila will not be late for school.
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December 3rd, 2016, 10:13 AM   #2
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For any two events $A,~B$

$P[A \cap B] = P[A | B] P[B]$

if $C$ and $D$ are mutually exclusive events (such as walking and cycling) then

$P[C \cup D] = P[C] + P[D]$

For two mutually exclusive events, $E,~F$ whose union is the entire sample space (again like walking and cycling).

$P[F] = 1 - P[E]$

from these you can work out this problem.
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