A committee of 5 is to be chosen from group of 9 people.Number of ways in which it can be formed if two particular persons either serve together or not at all and two other particular persons refuse to serve with each other is ..??

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Two parallel beams of light P and Q are incident normally on a prism and the transmitted rays are brought to focus with the help of a convergent lens as shown. If the intensities of the upper and lower beams immediately after transmission from face AC are 4I abd I, respectively, find the resultant intensity at the focus.

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The system of connected flexible cables shown in the figure is supporting 2 loads of 550N and 600N at points B and D. Determine the tensions in various segments of the cable