Round table

A tablecloth should be sewn on a round table with a diameter of 78 cm, which should extend around the table by 10 cm. How many cms of ribbons need to be bought for edging?

Correct result:

x =  307.9 cm

Solution:

$$\begin{gathered} D=78\text{ cm } \\ a=10\text{ cm } \\ r=D\mathrm{/}2=78\mathrm{/}2=39\text{ cm } \\ {r}_2=r+a=39+10=49\text{ cm } \\ x=2\pi \cdot r_2=2\cdot 3.1416\cdot 49=307.9\text{ cm} \end{gathered}$$

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