A drawer contains white socks and black socks only.
The number of white socks to the number of black socks is in the ratio 1:3 There are 12 white socks. How many black socks are in the drawer

Aparticular telephone number is used to receive both voice calls and fax messages. suppose that 25% of the incoming calls involve fax messages, and consider a sample of 25 incoming calls. (a) what is the expected number of calls among the 25 that involve a fax message?