There are $x$ trees and $y$ parrots. If in each tree only one parrot is sitting, then one parrot remains without a tree. If in each tree, two parrots are sitting, then one tree remains without a parrot. Therefore, $x$ and $y$ are respectively
(a)3 and 4
(b)4 and 5
(c)5 and 6
(d)6 and 7
Answer
Answer (as printed): A
Explanation
Clearly, we have: $$x+1=y \Leftrightarrow x-y=-1$$ And, $2(x-1)=y \Leftrightarrow 2 x-y=2$ Subtracting (i) from (ii), we get: $x=3$. Putting $x=3$ in $(i)$, we get: $y=4$.
Explanation as extracted from the printed page; notation may be imperfect.