A road is 4 km 800 m long. If trees are planted on both its sides at intervals of 9.6 m, how many trees were planted?

Total length of the road = 4 km 800 m = 4 km + 800 m = 4000 m + 800 m = 4800 m (1 km = 1000 m)

Distance between two plants = 9.6 m

∴ Number of trees planted on each side of the road = (Total length of the road ÷ Distance between two plants) + 1

= (4800 m ÷ 9.6 m) + 1

= $\left(\frac{4800}{1}÷\frac{96}{10}\right)$ + 1

= $\left(\frac{4800}{1}\times \frac{10}{96}\right)$ + 1

= 500 + 1

= 501

∴ Total number of trees planted on both sides of the road = Number of trees planted on each side of the road × 2 = 501 × 2 = 1002

Thus, the number of trees planted on both sides of the road is 1002.