Here according to the problem description, "

the average grows by K" --> which implies that the new average will be "

L+k"

Solution :

Let's assume the value of new element to be "a". So converting the word problem into equation,

(19*L + a) / (19 + 1) = L + k ==> after solving the equation we will get a (value of newly added element) = L + 20K

But according to the answer options, problem writer wanted to convey "

k% percent rise in average value " .

If we consider this case than resulting equation will be,

(19*L + a) / ( 19+1 ) = L + (K/100)*L ==> 19L + a = 20 [ L + KL/100]

==> a= 20L + KL/5 -19L

==> a= L + KL/5 , which is equivalent to option [A]

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