Switch A turns lights 1 and 2 on/off or off/on. Switch B turns lights 2 and 4 on/off or off/on. Switch C turns lights 1 and 3 on/off or off/on. Switches C, A and B are thrown in turn with the result that Figure 1 turns into Figure 2. Which switch does not work at all?
A man has 53 socks in his drawer: 21 identical blue, 15 identical black and 17 identical red. The lights are fused and he is completely in the dark. How many socks must he take out to make 100 per cent certain he has a pair of black socks?
Find five consecutive digits in the row below that total 22: 7 3 9 6 4 1 3 7 9 3 5 4 1 7 6 5. Enter the five digits in order as one number (e.g. 12345).
Switch A turns lights 1 and 2 on/off or off/on. Switch B turns lights 2 and 4 on/off or off/on. Switch C turns lights 1 and 3 on/off or off/on. Switch D turns lights 3 and 4 on/off or off/on. Switches D, C, A and B are thrown in turn, with the result that Figure 1 turns into Figure 2. Which switch does not work at all?
A market stall owner found that 72 eggs in a consignment were cracked, which was 12 per cent of the total consignment. How many eggs in total were in the consignment?
A B C D E F G H
What letter is two letters to the left of the letter immediately to the right of the letter three letters to the right of the letter A?
The cost of an identical three-course lunch for four people was £56.00. The main course cost twice as much as the sweet, and the sweet cost twice as much as the starter. How many pounds did the main course cost per person?
Three teams, from England, Scotland and Wales, are competing for two trophies, one for golf and one for tennis. How many different outcomes of the two competitions exist?
Switch A turns lights 1 and 2 on/off or off/on. Switch B turns lights 2 and 4 on/off or off/on. Switch C turns lights 1 and 3 on/off or off/on. Switch D turns lights 3 and 4 on/off or off/on. Switches B, D, A and C are thrown in turn, with the result that Figure 1 turns into Figure 2. Which switch does not work at all?
