4. Which of the following is not a multiple of 5?

5**. **Which of the following numbers is the largest?

7. The circles *P, Q* and *R* are all tangent to each other. Their centres all lie on a diameter of *P*, as shown in the figure.

What is the value of $\frac{circumference of *Q* + circumference of *R*}{circumference of P*}*$ ?

12. A regular tetrahedron is a polyhedron with four faces, each of which is an equilateral triangle, as shown. A solid regular tetrahedron is cut into two pieces by a single plane cut.

Which of the following could *not *be the shape of the section formed by the cut?

15.A square is inscribed in a circle of radius 1. An isosceles triangle is inscribed in the square as shown.

What is the ratio of the area of this triangle to the area of the shaded region?