A rectangular plot measuring 90 metres by 50 metres is to be enclosed by wire fencing. If the poles of the fence are kept 5 metres apart, how many poles will be needed?  Choose the most appropriate option:
A) 55	B) 56	C) 57	D) 58	E) none of these

Rationale: "solution perimeter of the plot = 2 ( 90 + 50 ) = 280 m . ∴ number of poles = [ 280 / 5 ] = 56 m answer b"
Answer: B