Ratio of wavelengths when a bright fringe of one coincides with a dark fringe of the other

1. A.
   $\frac{m-1}{n}$
2. B.
   $\frac{2m-1}{n}$
3. C.
   $\frac{2m-1}{2n}$
4. D.
   $\frac{2m+1}{2n}$

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1. A.
   $\frac{7}{9}$
2. B.
   $\frac{10}{11}$
3. C.
   $\frac{11}{10}$
4. D.
   $\frac{9}{7}$

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1. A.
   $\frac{9}{7}$
2. B.
   $\frac{7}{9}$
3. C.
   $\frac{10}{11}$
4. D.
   $\frac{11}{10}$

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1. A.
   $\dfrac{m}{n - 1}$
2. B.
   $\dfrac{m}{(2n - 1)}$
3. C.
   $\dfrac{2m}{(2n - 1)}$
4. D.
   $\dfrac{2m}{(2n + 1)}$

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