book Maths Puzzle Numerical Ability

Eight marbles look alike, but one is slightly heavier than the others. Using a balance scale, explain how you can determine the heavier one in exactly 2 weighings.

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book Other Question

This is about factoring.

With this problem I had to factor out the greatest common factor, then factor the remaining polynomial if possible: then check it.

so here's the p x^2-3x -23=5
(x^2-3x -23-5)=0
(x^2-3x-23-5)=0
(x^2-3x-28)=0
x^2 +4x -7x-28)=0
x(x+4)+ (-7) (x+4)=0
(x-7 (x+4)=0
(x-7)=0 or (x+4)=0
x=7 or x=-4