[Q.21] The length and breadth of a rectangle are increased by 10% and 20% respectively. By what percentage does its area increase?
Net change % = a + b + (ab/100) = 10 + 20 + (10*20/100) = 32%.
[Q.22] If log_10(x) = 3, what is the value of x?
$x = 10^3$ = 1000.
[Q.23] The probability of drawing a red card from a standard deck of 52 playing cards is:
Number of red cards = 26. P(Red) = 26 / 52 = 1/2.
[Q.24] Three numbers are in arithmetic progression (AP). If their sum is 15, what is the middle number?
Sum of 3 terms in AP = 3 * (middle term) = 15 => middle term = 5.
[Q.25] Simplify: $(x^3 - y^3) / (x - y)$ for x != y
Standard identity factorization: $x^3 - y^3$ = (x - $y)(x^2 + xy + y^2)$.