If two's company, and three's a crowd, what are four and five?
How many days are there in 4 years
1460 or 1484days
One out of 9 otherwise identical balls is overweight. How can it be identified after 2 weighings?
Weigh a group of 3 balls against another group of 3, then you'll know which group of 3 contains the heavy ball. Pick 2 balls from that group and weigh one against the other.