Total # outcomes when the die is thrown 3 times = 6 x 6 x 6
Favorable outcomes:Logic
- The range of the numbers is 3.
- The numbers obtained, when arranged in ascending order are
a, _, a+3.- What could the middle term be? Anything from a to a+3, both included (a, a+1, a+2, a+3)
There are only a few possibilities for what these numbers can be ->
(1) 1, 1/2/3/4, 4
(2) 2, 2/3/4/5, 5
(3) 3, 3/4/5/6, 6
No other possibilities.
But also remember - we also need to count the possible arrangements of numbers within every possible case above.
For example --- (1, 2, 4) is different from (4, 2, 1). Our total outcomes (6 x 6 x 6) counts these two as separate. So, when calculating favorable outcomes, we need to count all possible arrangements too.
Calculationa, _, a+3
(1) How many ways to select "a"?
3 (Because "a" can only be 1 or 2 or 3).
(2) Once the lowest number "a" is chosen, there is only
1 possibility for the highest number "a+3".
(3) Based on which middle term is selected, the number of arrangements varies. So, let's break this down.
a) If the middle term is "a", then the numbers obtained are (a, a, a+3). There are 3!/2! = 3 total arrangements.
b) If the middle term is "a+3", then the numbers obtained are (a, a+3, a+3). There are 3!/2! = 3 total arrangements.
c) If the middle term is "a+1", then the numbers obtained are (a, a+1, a+3). There are 3! = 6 total arrangements.
d) If the middle term is "a+2", then the numbers obtained are (a, a+2, a+3). There are 3! = 6 total arrangements.
Either of the above 4 could happen. So, the total possibilities = 3 + 3 + 6 + 6 = 18.
#Favorable Outcomes = (1) x (2) x (3) = 3 x 1 x 18
Probability = Favorable/Total = \(\frac{(3 * 18) }{ (6 * 6 * 6)}\) =
1/4. Choice D.
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Harsha