Cranky mower To start her old lawn mower, Rita has to pull a cord and hope for some luck. On any particular pull, the mower has a 20% chance of starting. (a) Find the probability that it takes her exactly 3 pulls to start the mower. Show your work. (b) Find the probability that it takes her more than 10 pulls to start the mower. Show your work.

(a) = 0.128

(b) = 0.1074

Step-by-step explanation:

Probability of starting the mower = 20%

Probability of  not starting the mower = 80%

(a) In order to take her exactly three tries, the mower should not turn on with the first two attempts but turn on with the third attempt:

(b) The probability that it takes her more than 10 pulls to start the mower is given by the probability of 10 straight failed attempts happening:

by definition, an arc subtended by a central angle of some given measure has the same measure. so .