# 25

= 5 × 5
A square.

= 1 + 3 + 5 + 7 + 9
= 3 + 4 + 5 + 6 + 7

= 32 + 42
A square number which is the sum of two square numbers.

25 is the sum of the first five odd numbers.

25 per cent means one quarter.

In the USA a quarter is a 25 cent piece worth a quarter of a dollar.

December 25 is Christmas Day.

A silver anniversary celebrates 25 years.

In the UK a pony is slang for 25 pounds.

The M25 is an orbital motorway around London. It is affectionately known as the longest car park in the world.

Pachisi, the Hindu word for 25, is one of the national games of India.

This large cactus has 25 lines radiating from its centre.

In the UK, television is transmitted at the rate of 25 pictures a second or 90,000 pictures in a one hour programme. In the cinema, films are usually projected at a slower speed of 24 frames a second. In fact each picture is flashed twice on to the screen as this reduces the sensation of flicker for the viewer.

The film Jurassic Park consists of about 182,880 separate pictures. How long does the film last in the cinema at 24 pictures a second? How much shorter would it be if it was shown continuously on television at 25 pictures a second?