This was tricky, but this is how I solved it
Let
\(D_x\)= Total distance driven by over age 25
\(D_y\)= Total distance driven by under age 25
\(N_x\)= Number of drivers over age 25
\(N_y\)= Number of drivers under 25
\(T_x\)= Total number of tickets given to drivers over 25
\(T_y\)= Total number of tickets given to drivers under 25
1. Average miles driven
Average miles driven by over 25 = 2/3* Average miles driven by under 25
\(D_x\)/\(N_x\)= 2/3*\(D_y\)/\(N_y\)
\(D_x\)/\(D_y\)= 2/3*\(N_x\)/\(N_y\)
2. Speeding tickets per 10,000
Number of tickets received per distance by under 25 year olds = 8/5* Number of tickets received per distance by over 25 year olds ; note here that the question says 3/5 MORE tickets which is equivalent to 8/5 of the tickets.
\(T_y\)/\(D_y\)= 8/5*\(T_x\)/\(D_x\)
\(D_x\)/\(D_y\)= 8/5*\(T_x\)/\(T_y\)
3. Proportion of tickets received by drivers over 25 to total
From the question: Drivers over 25 receive 3/4 of all the speeding tickets issued.
\(T_x\)/\(T_x\)+\(T_y\)= 3/4
4\(T_x\)= 3\(T_x\)+3\(T_y\)
\(T_x\)/\(T_y\)= 3/1
Now:
from 2, we know that
\(D_x\)/\(D_y\)= 8/5*\(T_x\)/\(T_y\)
from 1, we also know that
\(D_x\)/\(D_y\)= 2/3*\(N_x\)/\(N_y\)
Substituting the total distance driven by number of drivers from 1 in 2
2/3*\(N_x\)/\(N_y\) = 8/5*\(T_x\)/\(T_y\)
we know from 3 that \(T_x\)/\(T_y\)= 3/1
therefore,
2/3*\(N_x\)/\(N_y\) = 8*3/5*1
\(N_x\)/\(N_y\) = 8*3*3/5*2
from the question we know that the total number of drivers over 25 = 108,000; substituting
108,000/ \(N_y\) = 8*3*3/5*2
\(N_y\) = 108,000*5*2/ 8*3*3
\(N_y\) = (12,000*5*2)/8
\(N_y\) = (12,000*5)/4
\(N_y\) = 3,000*5
\(N_y\) = 15,000
answer is B
kevincan
In Pittfield, drivers over the age of 25 drive, on average, two-thirds as many miles per year as drivers under 25. Drivers under 25 are given, on average, 3/5 more speeding tickets per 10,000 miles driven than drivers over 25. If the 108,000 drivers over 25 are given 3/4 of all speeding tickets issued in Pittfield, how many drivers in Pittfield are under 25?
A. 13,500
B. 15,000
C. 33,750
D. 36,000
E. 40,000