What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7?
(A) -0.72
(B) -1.42
(C) -1.98
(D) -2.40
(E) -2.89
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An open Blog with tentative solutions and discussion of GMAT questions
Blogue para afixar e discutir a resolução de exercícios do GMAT
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6 comments:
Thinking about solving the polynomial for x=0.7? No way. If you observe the (exact) results you notice you have two decimals. You wopuld also notice that anly options (A) and (B) have the same value at the hundredths (2). So we might be lucky... just looking into that position in the result. For x=0.7 we get 2x^2=2x(*.*9)=*.*8; the term -2.4x yields inthe hundredths the lest significant digit of -0.4 times 0.7, thus -*.*8. As the third term is zero in the hundredths, the result will be *.*8 - *.*8 - *.*0 = *.*0, that is with a zero at the hundredths digit.
Fortunately, this situation only occurs with the option... (D)
* stands for a "d'ont care" digit
The question is incorrect. It should be 2x^2 instead of 2x^3.
Where we read 2x^3 - 2.4x - 1.7 for x = 0.7
we must read 2x^2 - 2.4x - 1.7 for x = 0.7
Or the answer is - 2.694
Olá! A questão está diferente da resolução na primeira parcela da equação:
No problema temos 2x^3 enquanto q na resolução foi usado 2x^2.
Apenas uma observação.. o site é muito bom. Bom trabalho!!
Hum! Well I belive the formula is wrong on the problem's equation... Tried for a few minutes before viewing the solution and noticed you mention here 2x^2 and in the question the formula mentions 2x^3... :D
Great blog you have here! ;)
*** THE QUESTION WAS WRONG, YES!* ***
Thinking about solving the polynomial for x=0.7? No way. If you observe the (exact) results you notice you have two decimals. You would also notice that only options (A) and (B) have the same value at the hundredths (2). So we might be lucky... and it could just be enough to look into that position in the result. For x=0.7 we get 2x^2=2x(*.*9)=*.*8; the term -2.4x yields in the hundredths the least significant digit of -0.4 X 0.7, thus -*.*8. Because the third term in the hundredths is zero, the result will be *.*8 - *.*8 - *.*0 = *.*0, that is with a zero at the hundredths digit.
Fortunately, this situation only occurs with the option... (D)
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* thank you, dear readers, for having pointed out this strange case of a right answer for a wrong question! :-)
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