Hi Bunuel!

I understand how we have arrived at 15. Here, we assume that the distance from a city to another city is the same even when the origin and destination is flipped.

But, there is a possibility to travel from City A to City B in 5 Kilometers and from City B to City A in 10 kilometers (since the route is a one way or something). The question merely asks what the least number of table entries must be and not the least number of table entries in the shortest possible route (which could remove the possible assumption that there are no one ways). So, shouldn't the answer be 30?

Bunuel wrote:

eybrj2 wrote:

In the table above, what is the least number of table entries that are needed to show the mileage between each city and each of the other five cities?

A. 15

B. 21

C. 25

D. 30

E. 36

Sorry for the messy picture..

The least number of table entries will be if we use only one entry for each pair of the cities. How many entries would the table then have? Or how many different pairs can be selected out of 6 cities?

\(C^2_{6}=15\)

Answer: A.

Similar question to practice:

each-dot-in-the-mileage-table-above-represents-an-entry-95162.htmlHope it helps.

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Cheers!!

JA

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