I just started reading Fractions in Realistic Mathematics Education by Leen Streefland, and there, on page 5, Streefland gives as an example an old puzzle problem that I remember giving my students more than 40 years ago.
“An old Arab, Anwar his name, decreed before he died that his eldest son inherit one-half, his second son one-quarter, and his youngest son one-fifth of all his camels. He died leaving 19 camels and his three sons could not agree on how to divide them. A dervish–passing by on his camel–observed the disagreement, dismounted, and stated helpfully, “I will loan you my camel.” Each son now took his share of the 20 camels. The dervish then remounted his beast of burden and continued along his way, leaving all three heirs contented. And so did come to pass the last will of Anwar.”
What’s going on? What do you notice? What are you wondering?