A rectangular hall, 142 metre long, is paved with 12425 tiles, each measuring 8 $$\text{dm}^2$$​ (decimetre square). The width of the hall is:

Correct option is D

Given:

The length of the hall is 142 meters.

The total number of tiles used is 12425.

The area of each tile is 8 dm² (decimeter square).

We have to find the width of the hall.

Formula  Used:

$$\text{Total area covered by tiles} = \text{Number of tiles} \times \text{Area of each tile}$$

$$\text{Area of the hall} = \text{Length} \times \text{Width}$$ 

Convert the area of each tile to square meters: 

​$$\text{dm}^2 = 0.01 \, \text{m}^2$$

Solution:

​the area of each tile in square meters is:

8 $$\text{dm}^2 = 8 \times 0.01 = 0.08 \, \text{m}^2$$​​

​$$\text{Total area} = 12425 \times 0.08 = 994 \, \text{m}^2$$​​

​$$\text{Area of the hall} = = 142 \times \text{Width}$$​​

​$$994 = 142 \times \text{Width}$$​​

​$$\text{Width} = \frac{994}{142} = 7 \, \text{meters}$$​​

The width of the hall is: 7 m

Thus, the correct option is (d) 7m.