L's All Around
Geometry
Level
3
How many normal L triominos can fit in a seven-by-seven grid?
12
13
14
15
16
more than 16
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7 × 7
= 49
= 4 × 12 + 1
= 4 × (3 × 4) + 1
It's easy to fix 4 triominos in 3-by-4 grid using 2 stacks of 2 'hugging' / Ying–Yanging triominos. Then, this configuration can be fitted in the 4 corners of 7 × 7 grid board by the use of rotation symmetry since 7 = 3 + 4, just leaving the single central grid as a hole (the + 1).