Question 8
The beavers put 13 balls in a triangular box as illustrated below.
A ball is said to be in a “dangerous” position if it satisfies at least two of the following conditions:
- There is at least one empty space immediately below it.
- There is at least one ball immediately below it that is in a dangerous position.
How many balls in the box are not in a dangerous position?
Editorial clarification approved for this practice package: the original wording above is preserved. For grading, interpret the two danger conditions with “at least one” (OR), as used in the official solution, rather than “at least two” (AND). The bottom edge of the box supports its bottom row.
A ball is said to be in a “dangerous” position if it satisfies at least two of the following conditions:
- There is at least one empty space immediately below it.
- There is at least one ball immediately below it that is in a dangerous position.
How many balls in the box are not in a dangerous position?
Editorial clarification approved for this practice package: the original wording above is preserved. For grading, interpret the two danger conditions with “at least one” (OR), as used in the official solution, rather than “at least two” (AND). The bottom edge of the box supports its bottom row.