This grid gives a visual way of calculating the answer to the question, “Among families that have two children, one of whom is a boy born on a Tuesday, how many have two boys?” It shows all the possible variations of birth day and gender for children in a two-child family. The families with the saturated colors are those which might qualify, while those that are shaded out are eliminated.
The row gives the birth day of the older child and the column gives the birth day of the younger, while the color represents the sex of each child. If the older child is a boy born on Tuesday, then the family must lie on the Tuesday row and the box representing the older child must be blue. If the younger child is a boy born on Tuesday, the family must lie on the Tuesday column and the box representing the younger child must be blue. The combination of all those boxes show all the possible families that qualify.
The total number of saturated boxes is 27. The number of saturated boxes in which both children are boys is 13. So the probability is 13/27.
Credit: Bill Casselman
Eruption early in human prehistory may have been more whimper than bang
Greed may breed financial fitness, but evolution allows unselfishness to survive
Fine-tuning of technique used in other animals could enable personalized medicine
Simulation suggests long-term effect on sea level not as dire as some predictions
Coverage of the 2013 American Association for the Advancement of Science meeting
The Year in Science 2012
Three-part series on the scientific struggle to explain the conscious self
Tables of contents, columns and FAQs on SN Prime for iPad
Please alert Science News to any inappropriate posts by clicking the REPORT SPAM link within the post. Comments will be reviewed before posting.
You must register with Science News to add a comment. To log-in click here. To register as a new user, follow this link.