||Bettina took 11 lessons.
Let A stand for Abigail, B for Bettina, and
so on. C = 2B A = D + 4 = C - 3 D = 15
Since D = 15, you know that A = 19. You also
know that C - 3 = 19, which means that C = 22.
And since C = 2B, 22 = 2B, which means that B
Source: Inspired by a similar
puzzle inUnriddlingby Alvin Schwartz,
New York: Lippincott, 1983.