Question : The value of $\frac{1.6 \times 1.6 \times 1.6-0.6 \times 0.6 \times 0.6}{1.6 \times 1.6+1.6 \times 0.6+0.6 \times 0.6}$ is:

Question : Twenty-one times a positive number is less than its square. The value of the positive number is:

Question : A positive number, when decreased by 4, is equal to 21 times the reciprocal of this number. The number is:

Question : What is the sum of the first 20 terms of the following series?
$1 \times 2+2 \times 3+3 \times 4+4 \times 5+\ldots \ldots$

Question : The intensity of any wave is proportional to which of the following?