exam Maths Puzzle Numerical Ability

Which of the following are functions?Explain your reasoning.

f(x)=5 if x>0
f(x)=-5 if x<0
f(x)=5 or -5 if x=0

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exam Other Question

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5s^2+5s/35s^2+25s

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The US population in 1990 was approximately 250 million, and the average growth rate for the past 30 years gives a doubling time of 66 years. The formula for the U.S. becomes P(in