East African people like riddles. There is a large collection of classical riddles which every child learns by heart. But there are many more created every day. It is quite common for people sharing a walk in the streets or gathered around a bonfire to test each other with riddles. The person who intends to quiz others will exclaim: Kitendawili! Prompt will be the answer: Tega!, which challenges the proponent. Each in the group will have a right to present a riddle. Other times, people gather to chemsha bongo, literally ‘to boil the brain’.
During these sessions people can propose riddles, mysteries in need of a solution, or short stories with unexpected endings. During one of these sessions, Njoroge asked his grandchildren to solve his riddles. Kariuki was quite good on remembering the old ones, the ones he heard in the many evenings spent at his grandfather homestead. Kamau was smart in solving brainteasers with a twisted logic, he was shrewd. Wanjiku knew many answers, but she was growing tired of the usual kitendawili.
Just before retiring for the night, Njoroge said, ìI have one more puzzle to solve. I shall put a hat on each of you. The hat will be either red or blue. You will be able to see the hats of your siblings, but not your own. The one who will be able to tell me which colour his hat is, that one will win tonight’s chemsha bongo! He then got up and put a red hat on each of his grandchildren while they kept their eyes shut.When old Njoroge sat down again, he asked the trio to open the eyes. ìIf any of you sees a red hat, he should raise his handî. Like a flash, all of them shot up their hand. ‘Very well, said Njoroge, so at least one of you has a red hat. But, pray, tell me the colour of the hat you are wearing’.
For a while they all sat in silence. Then Wanjiku raised her hand once again. ‘Say, Wanjiku, what colour is your hat?. I am wearing a red hat’, she said. She was right and she won the contest. How did she know the right answer?
Wanjiku reasoned as follow: There should be at least one red hat, but there could be three as well. I see two red hats on the heads of my brothers. If my hat were blue, then Kariuki – who saw the red hat of Kamau and my blue one – would have known he was wearing a red hat. Otherwise he could not explain why Kamau raised his hand to say he saw a red hat. Kamau should be thinking the same. However, since neither is able to solve the riddle, it means they see a red hat on my head too. So I am wearing a red hat!