Question

find the missing dimension. use the scale factor 1:12.
item model actual
football helmet diameter:□mm diameter:21 cm

Explanation:

Step1: Convert actual diameter to mm

Since \(1\ cm = 10\ mm\), then \(21\ cm=21\times10 = 210\ mm\).

Step2: Use the scale factor

The scale factor is \(1:12\), which means \(\frac{\text{Model dimension}}{\text{Actual dimension}}=\frac{1}{12}\). Let \(x\) be the model diameter. Then \(x=\frac{210}{12}\).

$$x=\frac{210}{12}=\frac{35}{2}=17.5$$

Answer:

\(17.5\)