What is the perimeter of the shaded region in a 3×3 grid where some 1×1 squares are shaded?
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.
Solution
The top, left and bottom unit squares each contribute 3 sides of length 1 to the perimeter. The remaining square contributes 1 side of length 1 to the perimeter. Therefore, the perimeter is 3×3+1×1=10.
Want a route through all this instead of an archive? The track
puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.
Source: Omni-MATH,
licensed Apache-2.0.
Statement and solution reproduced as published; topic and difficulty added by this site.