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Higher June 2023 Unit 1 Q7

WJECHigherCurrent spec5 marksTree Diagrams

7. Whitney walks, cycles or travels on the bus to work each day.

On any randomly chosen day:

  • the probability that she walks to work is 0·25
  • the probability that she cycles to work is 0·45.

At work, the probability that there will be a fire drill on any randomly chosen day is 0·04.

How Whitney travels to work is independent of whether or not there is a fire drill.

(a) Complete the tree diagram shown below. [3]
Tree diagram: Travel to work branches Walk 0.25, Cycle 0.45, Bus blank; then Fire Drill branches Yes 0.04 and No blank after each
(b) On a randomly chosen day, what is the probability that Whitney walks to work and there is a fire drill? [2]