A piece 13

A piece of plank 2 1/2 cm thick is glued to another piece, which is 1 3/4 cm thick, to form a tabletop. Find the thickness of the tabletop if the glue used is 1/5 cm thick. primary school

Correct answer:

x =  4 ⁹⁄₂₀ = 89/20 cm

Step-by-step explanation:

$$\begin{gathered} a=2\frac{1}{2}=2+\frac{1}{2}=\frac{2\cdot 2+1}{2}=\frac{4+1}{2}=\frac{5}{2}=2.5\text{cm} \\ b=1\frac{3}{4}=1+\frac{3}{4}=\frac{1\cdot 4+3}{4}=\frac{4+3}{4}=\frac{7}{4}=1.75\text{cm} \\ c=1/5=\frac{1}{5}=0.2\text{cm} \\ x=a+b+c=\frac{5}{2}+\frac{7}{4}+\frac{1}{5}=\frac{50}{20}+\frac{35}{20}+\frac{4}{20}=\frac{50+35+4}{20}=\frac{89}{20}=\frac{89}{20}\text{cm}=4\frac{9}{20}\text{cm}=4.45\text{cm} \end{gathered}$$

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