(i) 243 = __3 x 3 x 3__ x 3

Here, two 3s are left which are not in a triplet. To make 243 a cube, one more 3 is required.

In that case, 243 × 3 = __3 × 3 × 3__ × __3 × 3 × 3__ = 729 is a perfect cube. Hence, the smallest natural number by which 243 should be multiplied to make it a perfect cube is 3.

(ii) 256 = __2 × 2 × 2__ × __2 × 2 × 2__ × 2 × 2

Here, two 2s are left which are not in a triplet. To make 256 a cube, one more 2 is required. Then, we obtain

256 × 2 = __2 × 2 × 2 __× __2 × 2 × 2__ × __2 × 2 × 2__ = 512 is a perfect cube. Hence, the smallest natural number by which 256 should be multiplied to make it a perfect cube is 2.

(iii) 72 = __2 × 2 × 2__ × 3 × 3

Here, two 3s are left which are not in a triplet. To make 72 a cube, one more 3 is required. Then, we obtain

72 × 3 = __2 × 2 × 2__ × __3 × 3 × 3__ = 216 is a perfect cube. Hence, the smallest natural number by which 72 should be multiplied to make it a perfect cube is 3.

(iv) 675 = __3 × 3 × 3__ × 5 × 5

Here, two 5s are left which are not in a triplet. To make 675 a cube, one more 5 is required. Then, we obtain

675 × 5 = __3 × 3 × 3__ × __5 × 5 × 5__ = 3375 is a perfect cube. Hence, the smallest natural number by which 675 should be multiplied to make it a perfect cube is 5.

(v) 100 = 2 × 2 × 5 × 5

Here, two 2s and two 5s are left which are not in a triplet. To make 100 a cube, we require one more 2 and one more 5. Then, we obtain

100 × 2 × 5 = __2 × 2 × 2__ × __5 × 5 × 5__ = 1000 is a perfect cube Hence, the smallest natural number by which 100 should be multiplied to make it a perfect cube is 2 × 5 = 10

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