Some check!
Joe has been teaching Penny all about 鈥渃hecksums鈥�, which have been used for years to check the accuracy of calculations.
To calculate the checksum of a number you add up its digits. If that total is a single digit then that is the checksum; if not, the digits in the total are added to produce a new total and the process is repeated until a single-digit answer is produced. That single digit is the original number鈥檚 checksum.
What is the checksum of the number (2100 + 3200)300?
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WIN 拢15 will be awarded to the sender of the first correct answer opened on Wednesday 7 October. The Editor鈥檚 decision is final. Please send entries to Enigma 1561, New 女生小视频, Lacon House, 84 Theobald鈥檚 Road, London WC1X 8NS, or to enigma@newscientist.com (please include your postal address).
Answer to 1555 Not a square: The 2-digit number is 71
The winner Terry Lovekin of Scarborough, Ontario, Canada
