Math question (Need explanation)

Test Preparation ACT Preparation
1

<p>1,296 ACT practice questions book</p>

<p>Question 16.
The percent P of a population that has completed 4 years of college is given by the function P(t)= 0.001t*2 + 0.4t
where t represents time, in years. What percent of the population have completed four years of college after 20 years, to the nearest tenth?</p>

<p>Answers
F. 0.1
G. 7.6 (right answer)
H. 8.0
J. 8.4 (my answer)
K. 160.0</p>

<p>Books explanation
To find percent P, Substitute 20 for t to calculate -0.001(20)<em>2 + 0.4(20)=7.6. Choice(F)is the rounded value of 0.076%, which is not equivalent to 7.6%. Choice (H) and (J) result if you don’t pay attention to PEMDAS or distribution of the negative sign. Choice (K) results if t</em>2 and t are switched.</p>

<p>My question is, Where does this negative sign come in from? Can someone better explain that to me? :)</p>

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<p>Negative sign comes from a typo and failure on the book’s part. The correct answer is 0.001(20^2) + 0.4(20) = 8.4%.</p>

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<p>Wow, i wasnt expecting a typo in a book, especially an act practice test book lol. So the type is in the question?</p>

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<p>Some test preparation books are full of typos and bad questions. In this case they put a negative sign and <em>evaluated the expression with the negative sign,</em> yielding 7.6%.</p>