21 binders can bind 1400 books in 15 days. How many binders will required to bind 800 books in 20 days ?
A. 7
B. 9
C. 12
D. 14
E. None of these
Answer: Option B
Solution(By Examveda Team)
Let the required number of binders be xLess books, Less binders (Direct proportion)
More days, Less binders (Indirect proportion)
\[\left. \begin{gathered} {\text{Books 1400}}:800 \hfill \\ \,\,\,\,\,\,\,\,\,{\text{Days 20}}:15 \hfill \\ \end{gathered} \right\}::21:x\]
$$\eqalign{ & \therefore {\text{ }}1400 \times 20 \times x = 800 \times 15 \times 21 \cr & \Leftrightarrow x = \frac{{\left( {800 \times 15 \times 21} \right)}}{{\left( {1400 \times 20} \right)}} \cr & \Leftrightarrow x = 9 \cr} $$
Related Questions on Chain Rule
A. Rs. $$ {\frac{{{\text{xy}}}}{{\text{d}}}} $$
B. $${\text{Rs}}{\text{.}} {xd} $$
C. $${\text{Rs}}{\text{.}} {yd} $$
D. Rs. $$ {\frac{{{\text{yd}}}}{{\text{x}}}} $$
A. $$29\frac{1}{5}$$
B. $$37\frac{1}{4}$$
C. 42
D. 54
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