1. The probability that your mail is delivered before 2 pm is 0.9, so the probability that the mail is delivered at 2 pm or after 2 pm (so not before 2 pm) is 1-0.9=0.1.
Remark: 0.9=9/10=90/100=90%, and 0.1 is 10%
2. Probability of the mail being delivered before 2 pm for 2 consecutive days is
[tex] \frac{90}{100}* \frac{90}{100}= \frac{9}{10}* \frac{9}{10}= \frac{81}{100}=0.81 [/tex]
3. take a look at the picture attached, the tree diagram is another method we could use.
