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NDA 2013
Exam
NDA
Year
2013
Subject
Mathematics
Chapter
Determinants

NDA 2013 · Mathematics · Determinants

If 8 x-9 y=20 and 7 x-10 y=9 , then what is 2 x-y equal to?

If 8x−9y=208 x-9 y=20 and 7x−10y=97 x-10 y=9, then what is 2x−y2 x-y equal to?

Options

  1. A10
  2. B11
  3. C12
  4. D13

Correct answer

A. 10

Step-by-step solution

Substracting two given equations. 8x−9y=207x−10y=9−+−x+y=11 or, x=11−y\begin{aligned} 8 x-9 y & =20 \\ 7 x-10 y & =9 \\ -\quad+\quad & - \\ \hline x+y & =11 \quad \text{ or, } x=11-y \end{aligned} Plug in x=11−yx=11-y into 8x−9y=208(11−y)−9y=2088−8y−9y=20\begin{array}{r}8 x-9 y=20 \\ 8(11-y)-9 y=20 \\ 88-8 y-9 y=20\end{array}or, 17 y=68 \Rightarrow y=4and,and,x=11-4=72 x-y=2(7)-4=10$
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