There are 4 expression which can be combined 4C2 ways i.e. 6 ways.

Since this has only 6 ways, it always better to compute/write all the expressions. Mostly one gets these questions wrong because of hurry.

x+y, x+5y, x-y, 5x+y

(x+y) ( x+5y) = NOT

(x+y) ( x-y ) = YES x^2 - y^2

(x+y) (5x+y) = NOT

(x+5y)(x -y) = NOT

(x+5y) (5x+y)= NOT

(x-y)(5x+y) = NOT

Hence only 1 forms the required expression.

Probability = 1/6

hence E is the answer

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