This Exam P sample reference tests Equally Likely Outcome Counting. Among 36 ordered dice outcomes, 24 have absolute difference zero, one, or two. Thus the probability is 24/36=2/3, choice E.
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
Variant answer in brief
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.
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