In a row of people facing north, Chirag is 13th from the left end and Dolma is 8th from the right end. Chirag and Dolma are different people. What is the least possible number of people in the row?

13Correct answerYour answer14Correct answerYour answer20Correct answerYour answer21Correct answerYour answer

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CorrectNot quiteAnswer A

Correct answer: A

The row must hold at least 13 people, because Chirag is 13th from the left.
With exactly 13 people, Dolma 8th from the right is $13 - 8 + 1 = 6$ th from the left, a different place from Chirag's. So 13 works.
The least possible number is 13.

Worth noting

20 is $13 + 8 - 1$ , the total if Chirag and Dolma were the same person. When the positions may cross, the minimum is the larger of the two positions, provided they do not land on the same place.

Concept: Least row length when positions may cross
Typical timeTypical: 115 s
Your timeYours: —

The rule this testsPosition in a row

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Ten questions from Ranking and Ordering, at your own pace.

In a row of people facing north, Chirag is 13th from the left end and Dolma is 8th from the right end. Chirag and Dolma are different people. What is the least possible number of people in the row?

Explanation