My favourite book is All Quiet on the Western Front by Erich Maria Remarque. Memoirs of the First World War are often all gung-ho and Biggles, but this is written by a German soldier, and the misery and the fruitlessness of war come through. I like novels with description and emotion: early Ernest Hemingway (The Old Man and the Sea); John Steinbeck’s The Grapes of Wrath; Thomas Hardy. And Stephen King. I like the quickness of the story. Pet Sematary is great.

Family listening

I like 1970s music, particularly the Rolling Stones. Goat’s Head Soup is my favourite album. My son used to hate the Rolling Stones but he’s had to listen to them so often he likes them now.

Best on stage

It tends to be musicals, mostly Andrew Lloyd Webber. The best was Starlight Express. It’s a terrible story but great music. I like things if everybody around me is enjoying them. If I took my family to something I liked and they didn’t enjoy it, I wouldn’t like it either. But when I turn round and see someone really enjoying the show, especially children, it gives me such pleasure.

Playing the markets

My greatest interest, which fits in with my maths, is the stock market. I have belonged to an investment club for four years, so when I come home from school I’m straight on to the internet, checking up on the prices and wondering whether to buy or sell. I used to dabble and invest pound;500 at a time, but now it’s pound;5,000 at a time and I make a 30 per cent return. I invested my son’s university loan and made 30 per cent on that too.

I’ve worked out the percentages and I think I have a winning formula. I look for troughs and peaks and there’s a pattern to them. So if you watch for the pattern and pick the right shares, and you don’t tell anyone about it, you can always make money. But I never give anyone tips, because I couldn’t bear it if they invested money and lost it.

Treat in store

My wife has just given me a leaflet for a musical about Frank Sinatra and Dean Martin called The Rat Pack at the Strand Theatre in London, and I’m looking forward to that.

John Smith, 54, is head of maths at St Albans girls’ school. He was talking to Karen Gold