book Maths Puzzle Numerical Ability

please could you give me some simlpe inverse operation questions and answers? thank you

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book Other Question

what is the gradient of a line perpendicular to y=3x I am not sure if this is a quadratic equation question or not but here goes.

(1/w)+(1/(w-1))=(1/(w-w^2))

I am stumped. I think the answer is W=-1 but I have also gotten W=1