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Rectangle Rearrangement

Stage: 4 Short Challenge Level: Challenge Level:1

The diagram shows the two pieces will fit together to form a right-angled triangle which has a base $8$ and height $6$. The length of the hypotenuse = $\sqrt{(6^2+8^2)}$, that is $10$, so the perimeter of the triangle is $24$.
Rectangle solution

This problem is taken from the UKMT Mathematical Challenges.