Diamonds puzzle

The puzzle is composed of paper diamonds. One diamond has a tent 3.4 cm long and a corresponding height of 2.5 cm. How much paper in dm squared is needed for 60 diamonds?

Correct answer:

S =  5.1 dm²

Step-by-step explanation:

$$\begin{gathered} a=3.4\text{cm} \\ h=2.5\text{cm} \\ n=60 \\ {S}_1=a\cdot h=3.4\cdot 2.5=\frac{17}{2}=8.5{\text{cm}}^2 \\ {S}_2=S_1\to {\text{dm}}^2=S_1:100{\text{dm}}^2=8.5:100{\text{dm}}^2=0.085{\text{dm}}^2 \\ S=n\cdot S_2=60\cdot 0.085=5.1{\text{dm}}^2 \end{gathered}$$

Try another example