Example 4. Calculate: $\frac{3.6 \times 11.74 \times 138.4}{6 \times 2437}$.
(6 is an exact number)
\begin{aligned} & \text { Sol } \frac{3.6 \times 11.74 \times 138.4}{6 \times 2437} \\ \approx & \frac{3.6 \times 11.7 \times 138}{6 \times 2440} \approx \frac{0.60 \times 11.7 \times 138}{2440} \\ \approx & \frac{7.02 \times 138}{2440} \approx \frac{969}{2440} \approx 0.40 .\end{aligned}