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Odd, I must be making the exact same mistake.. I've done it several times now and I also keep coming up with 42..... Are you sure it was a mistake?
Yes, 21 cm is the correct length.
3 times the perimeter of a single trapezoid is 288 cm.
288-204 = 84cm. 84 cm corresponds to 4 times the length of PQ. Twice for the overlap between the top 2 trapezoids in Fig. 2 and twice for the overlap between the top left and the trapezoid just below in the same figure.
84/4=21 cm.
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Oh, I see where you made the mistake. You did actual math instead of just guessing 42....
Don't worry, it happens to the best of us.
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You got me ;)
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No worries, I will tag you when I have a question that requires 42 as the answer
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Splendid!
Sensei approves
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