Thirty students stand in a row facing north. Tanvi is 20th from the left end and Farhan is 17th from the right end. How many students stand between Tanvi and Farhan?

5Correct answerYour answer6Correct answerYour answer7Correct answerYour answer13Correct answerYour answer

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CorrectNot quiteAnswer A

Correct answer: A

Farhan's position from the left $= 30 - 17 + 1 = 14$ .
So Farhan (14th) is to the LEFT of Tanvi (20th): the positions cross.
Students between positions 14 and 20 are those at 15 to 19: $20 - 14 - 1 = 5$ .

Worth noting

7 comes from the shortcut $30 - (20 + 17)$ with the minus sign dropped; that shortcut works only when the two do not cross. Here $20 + 17 = 37$ is more than 30, the sign that they cross, and between $= 20 + 17 - 30 - 2 = 5$ .

Concept: People between two positions when the positions 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.

Thirty students stand in a row facing north. Tanvi is 20th from the left end and Farhan is 17th from the right end. How many students stand between Tanvi and Farhan?

Explanation