A’s salary is 40% more than B's. If B’s salary increases by 20% and A’s increases by x%, then A’s new salary becomes 25% more than B’s new salary. What is the value of x?

Correct — B. Take B's old salary as 100.

A's old salary = 100 + 40% of 100 = 140
B's new salary = 100 × 1.20 = 120
A's new salary = 120 × 1.25 = 150

A's rise = 150 − 140 = 10 on a base of 140
x = 10 ÷ 140 × 100 ≈ 7.14% → option (b).

Why the others are wrong

• (a)
  2.5% — 2.5% lifts A only to 140 × 1.025 = 143.5. That is about 19.6% above B's new 120, short of the 25% the question demands.
• (c)
  10.63% — 10.63% takes A to 140 × 1.1063 ≈ 154.9, past the 150 needed. A would then be about 29% above B's new 120, not 25%.
• (d)
  15.6% — 15.6% takes A to 140 × 1.156 ≈ 161.8, far past 150. The 25% condition pins A's new salary at 150, a rise of just 10 on 140.

Percentages of two people's salaries sit on different bases, so fix one salary as 100 and turn every statement into a number.

B = 100 makes A = 140. After B's 20% rise, B = 120, and A's new salary being 25% more than that pins it at 150.

The unknown x is A's own rise, so it is measured on A's old salary of 140, not on B's 100.

Key facts

• With B = 100: A = 140, new B = 120, new A = 150.
• x = (150 − 140) ÷ 140 × 100 = 100⁄14 ≈ 7.14%.
• p% more than Q means Q × (1 + p⁄100), so Q is the base.

Common traps

• Subtracting the percentages, 40% − 25% = 15%, as if both were taken on the same base.
• Measuring A's rise of 10 on B's old salary of 100 and getting 10%, when x is a percentage of A's own 140.

No directly related past PYQ was found.