Name: Ling
Who is asking: Student
Level of the question: All
Question: If an integer is randomly selected from all positive 2digit integers (i.e., the integers 10, 11, 12, . . . , 99), find the probability that the integer chosen has
(a) a 4 in the tens place
(b) at least one 4
(c) no 4 in either place

Ling,
There are 90 twodigit positive integers 10, 11, ..., 99. The ones that have a 4 in the tens place are 40,41,...,49. There are 10 such integers. Thus the probability that a twodigit number chosen at random will have a 4 in the tens place is
^{10}/_{90} = ^{1}/_{9 }
How many of the 90 twodigit integers have at least one 4? How many have no 4's?
Penny
