Answer:
- 36 cubes
- There are several forms to figure it out: see two different ways explained below.
Explanation:
The first way to figure out how many more cubes Jill will need to add to complete the structure until forming a rectangular prism is to add the cubes from column to colum,
The first column is complete: it has four rows each with 4 cubes.
The second column (the one next to the right of the first column) has three rows. Then Jill has to add one more row. This is 4 cubes.
The third column has two rows. Then, Jill will need to add two rows with 4 cubes each, for a total of 8 cubes. So far, the count is 4 + 8 = 12 cubes.
The fourth and fifth columns have just one row. Then, Jill will need 3 rows for each column, making it 2 × 3 × 4 = 24 cubes.
The total final count is 12 + 24 = 36 cubes. ← answer
There are different ways to figure out the number of cubes needed to complete the rectangular prism. This is another one:
How many cubes shall the complete pyramid have? : 4 × 4 × 5 = 80 (length × width × height).
How many cubes does the shown incomplete structure have?: 4×4 + 3×4 + 2×4 + 4 + 4 = 16 + 12 + 8 + 4 + 4 = 44.
Difference: 80 - 44 = 36 cubes. ← answer
