If P,Q,R are physical quantities, having different dimensions, which of the following combinations can never be a meaningful quantity ?

Q: If P,Q,R are physical quantities, having different dimensions, which of the following combinations can never be a meaningful quantity ?

(a) (P-Q)/R

(b) PQ-R

(c) PQ/R

(d) (R-Q)/P

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Ans: (a) & (d)

Physical quantity having same dimension can be added or subtracted .