Higher Plus

The point (20, 21) lies on the circle x² + y² = 841. Work out the gradient of the tangent to the circle at that point.The point (20, 21) lies on the circle x^2 + y^2 = 841. Work out the gradient of the tangent to the circle at that point.

A bag holds 7 red, 3 blue and 3 green counters. Two are taken without replacement. Given neither is green, what is the probability both are red?

A histogram has two bars: one 5 units wide with frequency density 0.4, one 20 units wide with density 3. How many values in total?

A block has mass 510 g (to the nearest 10 g) and volume 18 cm³ (to the nearest cm³). Work out the upper bound of its density, to 2 decimal places.A block has mass 510 g (to the nearest 10 g) and volume 18 cm^3 (to the nearest cm^3). Work out the upper bound of its density, to 2 decimal places.

In an algebraic proof, how would you write the next even number after 2n in terms of an integer n?