This is the sequence F7, F8, F9, F10, F11, F12, written backwards.
Often seen on a computer keyboard.
21F 11F 01F 9F 8F 7F
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Puzzle 7
Alex's child, Drew, is exactly one fifth of Alex's age. In 21 years, Alex will be exactly twice Drew's age. How old is Drew now? Billie is exactly seven times the age of his child, Glen. In 8 years, Billie will be three times the age of Glen. How old is Glen now?
The first ten prime numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29.
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