Six books are to be placed in a 3-tier triangular shelf. How many ways can this be done if the top teir can hold one book, the second tier can hold two books, the third teir can hold three books. (topic: permutation and combination)

The perimeter of a rectangle is greater than or equal to 74 meters. if the length is 25 meters, the minimum width of the rectangle is meters.

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?

Multiplying fractions by whole number 5 x 1/3=?