Mark the letter A, B, C or D on your answer sheet to indicate the word(s) CLOSET in meaning to the underlined word(s) in each of the following questions.

We decided to pay for the furniture on the installment plan.

A. credit card

B. cash and carry 

C. monthly payment

D. piece by piece

đăng linh tinh

olm trừ điểm đi

Đặt \(A=\dfrac{3}{1.2}+\dfrac{3}{2.3}+...+\dfrac{3}{2005.2006}\)

\(A=3\left(\dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{2005.2006}\right)\)

\(A=3\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{2005}-\dfrac{1}{2006}\right)\)

\(A=3\left(1-\dfrac{1}{2006}\right)\)

\(A=3.\dfrac{2005}{2006}\)

\(A=\dfrac{6015}{2006}\)

Ta có: A= \(\dfrac{1}{31}+\dfrac{1}{32}+...+\dfrac{1}{90}\)

\(A=\left(\dfrac{1}{31}+\dfrac{1}{32}+...+\dfrac{1}{60}\right)+\left(\dfrac{1}{61}+\dfrac{1}{62}+...+\dfrac{1}{90}\right)\)

A= B+C

Ta có: \(B=\dfrac{1}{31}+\dfrac{1}{32}+...+\dfrac{1}{60}>\dfrac{1}{60}+\dfrac{1}{60}+...+\dfrac{1}{60}\)

\(B=\dfrac{1}{31}+\dfrac{1}{32}+...+\dfrac{1}{60}>30.\dfrac{1}{60}=\dfrac{1}{2}\) (1)

Lại có: \(C=\dfrac{1}{61}+\dfrac{1}{62}+...+\dfrac{1}{90}>\dfrac{1}{90}+\dfrac{1}{90}+...+\dfrac{1}{90}\)

\(C=\dfrac{1}{61}+\dfrac{1}{62}+...+\dfrac{1}{90}>30.\dfrac{1}{90}=\dfrac{1}{3}\) (2)

Từ (1) và (2) => \(A>\dfrac{1}{2}+\dfrac{1}{3}=\dfrac{5}{6}\)

Vậy \(A>\dfrac{5}{6}\)