book Maths Puzzle Numerical Ability

-1/(w-1)+4+5/(w-4)=0

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book Other Question

0.5 percent of 80? A ROOM MEASURES 3M BY 4M BY 7M.
THE WALLS NEED 2 COATS OF PAINT. A 4-L CAN OF PAINT COVERS 40M SQUARED.
HOW MUCH PAINT SHOULD TANYA BUY?
I KNOW THE ANSWER BUT NOT HOW I GOT IT.