mm92325
I took 3 cities a,b and c now from a to b and c there will be 2 flights going to b and c and 2 flights coming back to a making 4 flight to and from a to other cities and similarly 4 flight for b and 4 flight for c making my total to 12
So 3 cities 12 flights giving me option B as correct, can you help me understand what is wrong here
gmatophobia
guddo
An airline serving n cities has 2 nonstop flights per day, one in each direction, between each pair of these cities. How many nonstop flights does the airline have among these n cities each day?
A. 2n(n-1)
B. n(n-1)
C. 2n^2
D. n^2
E. 2n
Attachment:
2024-01-27_20-58-23.png
One way to solve this question is by using the concept of Permutations and Combinations as Bunuel has depicted.
Another way is to assume a value of n and then eliminate the options.
Assume n = 2
The number of flights nonstop flights the airline has among these 2 cities ⇒ is 2 (one flight from City 1 to City 2 and another from City 2 to City 1
Answer choice elimination A. 2n(n-1) ⇒ 2 * 2 (1) = 4
B. n(n-1) ⇒ 2 * 1 = 2
C. 2n^2 ⇒ 2*2^2 = 8
D. n^2 ⇒ 2^2 = 4
E. 2n ⇒ 2 * 2 = 4
Option B
For 3 cities a, b, c, we have 3 pairs: (a, b), (a, c), (b, c). Each pair has 2 flights (one in each direction), so total = 3 * 2 = 6. Substituting n = 3 into choice B gives 3(3 - 1) = 6. So B is correct.