A rectangular sump of dimensions 6 m x 5 m x 4 m is to be built by using bricks to make the outer dimension 6.2 m x 5.2 x 4.2 m. Approximately how many bricks of size 20 cm x 10 cm x 5 cm are required to build the sump for storing water ?

Compute brick volume and the volume of mortarwork (outer minus inner). Volume of a cuboid is l×w×h, so outer volume = 6.2×5.2×4.2 = 135.408 m³ and inner (water) volume = 6×5×4 = 120 m³; brick-work volume = 135.408−120 = 15.408 m³ [1]. A single brick measures 20 cm×10 cm×5 cm = 0.2×0.1×0.05 = 0.001 m³ (use cm³↔m³ conversion: 1 cm³ = 1e−6 m³) [2]. Number of bricks ≈ 15.408 / 0.001 = 15,408. Hence option 3 is correct.

Sources

1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 9: The Amazing World of Solutes, Solvents, and Solutions > Activity 9.6: Let us calculate > p. 145
2. [2] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 9: The Amazing World of Solutes, Solvents, and Solutions > How to measure volume? > p. 143