Choose the correct statements:
A. x% of y is equal to y% of 100 x.
B. If 40% of 60% of of a number is 504, then 25% of of that number is equal to 350.
C. If A is 15% more than B, then B is ∼13.04% less than A.
D. 10% of 5 and 5% of 10 add-up to 0.1.
Choose the correct answer from the options given below:

Correct option is B

12/5Let's evaluate each statement, 
A. x% of y is equal to y% of 100 x.
x/100 × y = y/100 × 100 x
xy/100 = yx  (Incorrect)
B. If 40% of 60% of (35)(35)of a number is 504, then 25% of (25)(25)of that number is equal to 350.
Let's assume, the number is x.
40/100 × 60/100 × 3/5 x = 504
2/5 × 3/5 × 3/5 x = 504
x = 504 × 5 × 5 × 5 / 2 × 3 × 3
x = 3500
Now, 25% × 2/5 × 3500 = 350 ___ eqn.
Let's check LHS,
25 /100 × 2/5 × 3500
1/4 × 2/5 × 3500 = 350 = RHS (Correct)
C. If A is 15% more than B, then B is ∼13.04% less than A.
Suppose B is 100
A = 115/100 B 
A = 115/100 × 100
A = 115
Now, 
(A - B) × 100/A
(115 - 100) × 100/115
1500/115 = 13.04
So, B is ∼13.04% less than A.  (Correct)
D. 10% of 5 and 5% of 10 add-up to 0.1.
(10/100 × 5) + (5/100 × 10) = (.5 + .5) = 1 ( Incorrect)
Hence, the correct answer is "B and C only".