How many cubic blocks of side length 1/7 inch would it take to fill a cube with a side length of 3/7 inch?

Volume of the larger cube = (3/7) ^3=27/343 cubic units

Volume of the small cubes = (1/7) ^3=1/343 cubic units

Number of cubes=Volume of larger cube/Volume of small cubes

Number of cubes = (27/343) / (1/343) cubes = 27/1 = 27