The answers are choice B and choice C
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Mr Nemo has 5 desks while Mr Benn has 2 desks
We can say the following
number of desks Mr Benn has = (2/5)*(number of desks Mr Nemo has)
2 = (2/5)*(5)
2 = 2
Which basically is the math translation of "Mr Benn has 2/5 as many desks as Mr Nemo", so that's why choice C is one of the answers.
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Flip things around and we get
number of desks Mr Nemo has = (5/2)*(number of desks Mr Benn has)
5 = (5/2)*(2)
5 = 5
Note: 5/2 = 2 & 1/2
This is a translation from "there are 2 & 1/2 times as many desks in Mr Nemo's room as in Mr Benn's room" pointing to choice B as the other answer.