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$A, S, M$ and $D$ are functions of $x$ and $y$, and they are defined as follows:

• $A(x, y) = x + y$
• $S(x, y) = x - y$
• $M(x, y) = xy$
• $D(x, y) = x/y$,

where $y \neq 0$.

A man travels three-fifths of distance $AB$ at a speed of $3a$, and the remaining at a speed of $2b$. If he goes from $B$ to $A$ and back at a speed of $5c$ in the same time, then:

1. $1/a+1/b=1/c$
2. $a+b=c$
3. $1/a + 1/b=2/c$
4. None of these

### 1 comment

I think in question A(x,y) = x+y