Abag contains n counters.
one counter is blue and the rest are red.

two counters are taken at random from the bag.

express, in terms of n, the probability that a counter of each colour is taken.
give your answer as a fraction in its simplest form.

Apinhole camera is made out of a light-tight box with a piece of film attached to one side and pinhole on the opposite side. the optimum diameter d(in millimeters) of the pinhole can be modeled by d=1.9[ (5.5 x 10^-4) l) ] ^1/2, where l is the length of the camera box (in millimeters). what is the optimum diameter for a pinhole camera if the camera box has a length of 10 centimeters

Answer for 10 points show work you guys in advanced < 3

The measurement of one angle of a right triangle is 42° what is the measurement of the third angle? (there is no picture)