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A $6 \times 6$ board of squares is shown. How many rectangles drawn along its lines are NOT squares?

Competition practicePermutations & Combinations

A441
B350
C91
D256

Step-by-Step Solution

All rectangles:

^{7} C_{2} \times^{7} C_{2} = 21 \times 21 = 441

. Squares:

1^{2} + 2^{2} + \dots + 6^{2} = 91

. Non-squares:

441 - 91 = 350

.

Answer: B) 350

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