# How many segments are lit on a Seven Segment Digital Clock?

Ask Marilyn ® by Marilyn vos Savant is a column in Parade Magazine, published by PARADE, 711 Third Avenue, New York, NY 10017, USA. According to Parade, Marilyn vos Savant is listed in the "Guinness Book of World Records Hall of Fame" for "Highest IQ."

In her Parade Magazine column of July 2, 2006, Marilyn states that the last number in the sequence 19, 15, 18, 18, 17, 18, 19, 16, 20, 19, which repeats after 720 numbers, is 14, which represents 11:59 on a seven segment digital clock.

## Sorry, Marilyn

Ronald Niles ron@ronniles.com observed an inconsistency in Marilyn's answer:

Although Marilyn correctly recognizes the puzzle, the last number in the sequence, representing 11:59 is 15, not 14.

This could be simple mistake in math, but that is unlikely. More likely it is due to the different ways in which digital clocks represent the digit 9. Some use six segments to do it, and others omit the segment on the bottom, using only five. The former case would result in the last number in the sequence being 15, the latter case would result in 14. Since the reader who posed the question was clearly using a clock which uses six segments to represent the digit 9, the only correct interpretation of the last number in the sequence is 15.

http://www.wiskit.com/marilyn/sevensegment.html last updated August 9, 2006 by herbw@wiskit.com