Bunuel wrote:
Raffle tickets numbered consecutively from 101 through 350 are placed in a box. What is the probability that a ticket selected at random will have a number with a hundreds digit of 2 ?
(A) 2/5
(B) 2/7
(C) 33/83
(D) 99/250
(E) 100/249
Richlove wrote:
Please explain to me how the favorable cases inclusive are from 200 - 299 . Most especially the hundred digit of 2.
Richlove , I am not quite sure what you are asking.
Please be more specific next time?
I think your question involves inclusive counting.*
Favorable casesAny integer of the form 2 _ _ is a "favorable case"
How many of those 2 _ _ integers / terms are there?
• The first term in form "2 _ _" is 200
• The last term in the form "2 _ _" is 299
• Number of favorable cases? All the numbers from 200 to 299
• To find the number of favorable cases, use
inclusive counting formula:
(Last term - first term) PLUS ONESubtraction only, (Last - First), yields the
difference between integers
Subtraction does not yield the number of integers.
Take a small sample to see why
Small sampleHow many integers are there from 2 to 5?
2, 3, 4, 5: FOUR integers
But if we subtract? 5 - 2 = 3. Not correct
Add 1 to (5 - 2) = 3. Then (3 + 1) = FOUR integers
Counting: probabilityFor the problem, we need \(\frac{FavorableCases}{PossibleOutcomes}\)
Total possible outcomes?
All integers from 101 to 350
(350 - 101) =
249 + 1 =
250 all possible outcomes
(The box contains ALL the numbers: the 100s group, the 200s group, and the 300s group)
Favorable cases?
All the integers in the group with form 2 _ _
First term is 200, last term is 299
All integers in the 200s group?
(299 - 200) =
99 + 1 = 100 integers from 200 to 299
Probability?
Probability that you will pick a number from the 200s group?
\(\frac{Favorable}{Possible} = \frac{200s}{AllTickets'Numbers} = \frac{100}{250} = \frac{2}{5}\)
Answer C. Hope that helps.
*Other than "numbers that have hundreds digit of 2," what could be the "favorable cases" here? If you are asking why integers with 2 in the hundreds place are "favorable"? Because the prompt defines "numbers with a hundreds digit of 2" as "success."