Section B consists of 5 questions of 2 marks each.
21. If the system of equations \( 2 x+3 y=7 \) and \( (a+b) x+(2 a-b) y=21 \) has infinitely many solutions, then find \( a \) and \( b \).
OR
Sumit is 3 times as old as his son. Five years later, he shall be two and a half time as old as his son. How old is Sumit at present?
22. Write the coordinates of a point on \( x \)-axis which is equidistant from the points \( (-3,4) \) and \( (2,5) \).
23. \( X \) is a point on the side \( B C \) of \( \triangle A B C . X M \) and \( X N \) are drawn parallel to \( A B \) and \( A C \) respectively meeting \( A B \) in \( N \) and \( A C \) in \( M . M N \) produced meets \( C B \) produced at \( T \). Prove that \( T X^{2}=T B \times T C \).
24. Find the length of the tangent from an external point \( P \) at a distance of 20 cm from the centre of a circle of radius 12 cm .
OR
Two concentric circles are of radii 8 cm and 5 cm . Find the length of the chord of the larger circle which touches the smaller circle.
25. The probability of selecting a blue marble at random from a jar that contains only blue, black and green marbles is \( \frac{1}{5} \). The probability of selecting a black marble at random from the same jar is \( \frac{1}{4} \). If the jar contains 11 green marbles, find the total number of marbles in the jar.