ISI Kolkata professor gives the answer to the viral Donald Trump ‘COVFEFE’ question

“Note, here, time is not meant in the physical sense but counted by appearance of letters,” he wrote. Providing a background to the question, he added, “The original question comes from a classical exercise in the book of D Williams called Probability with Martingales. It says: in a random sequence of letters, drawn independently and uniformly from the English alphabetical letters, the expected time for the first appearance of the word “ABRACADABRA” is 26^11+26^4+26.”

In the case of COVFEFE, the proof can be done in many ways. In case you are confused, Hazra provides an example that might help you understand the solution.

“Say, in a casino, a person starts typing randomly. Now, a series of gamblers enter the casino one after the other. While the person in question types, the first gambler comes and bets Re 1 on the first word being C. If he wins then he bets again Rs 26 on the second letter being O, otherwise he loses all the money and quits the game.

“When the second letter is typed, another gambler comes in (who is unaware of the presence of the first gambler) and bets Re 1 on the second typed word being C. So again if this second gambler wins the bet he gets Rs 26. Each player continues betting until they lose and quit the game. This goes on and each gambler keeps on coming till the word COVFEFE appears. So if one thinks a bit then the sixth-to-last gambler will win and his total profit will be Rs 26^7.”

“Now here comes the “Martingale” part, which says that the game would be fair and the average profit will be zero. This means one wins and all others lose Re 1. The number of people losing money corresponds to the number of letters drawn before the word COVFEFE appears. So the expected time is 26^7.”

We wonder if Prof. Hazra would have an equation/theory about the next spelling mistake in POTUS’ tweet?!