Original practice · fully worked
Original variant: nearby outcomes on eight-sided dice
Two fair eight-sided dice, numbered 1 through 8, are rolled independently. Find the probability that the absolute difference between the two results is less than 2.
- A
1/8 - B
1/4 - C
5/16 - D
11/32 - E
3/8
Answer and calculation
There are 8 equal pairs and 14 adjacent ordered pairs, so 22 of 64 outcomes qualify. The probability is 11/32, choice D.
Setup
Setup
The two eight-sided dice produce 64 equally likely ordered outcomes.
N(Ω)=82=64 Model
Model
An absolute difference below two permits equal results and adjacent results only. There are eight equal pairs and fourteen ordered adjacent pairs.
N(∣D1−D2∣<2)=8+2(7)=22 Compute
Compute
Thus 22 of the 64 outcomes qualify, which reduces to eleven thirty-seconds.
Pr(∣D1−D2∣<2)=6422=3211 Answer
Answer
The probability is eleven thirty-seconds.
3211(D)