Successive percent changes on average speed A car's average speed is 75 km/h. It is first decreased by 40%, then increased by 50%. What is the new average speed?

Introduction / Context:
Successive percentage changes multiply, not add. After reducing a quantity by p% and then increasing by q%, the net factor equals (1 − p/100) * (1 + q/100) applied to the original value.

Given Data / Assumptions:

• Initial speed = 75 km/h.
• Decrease by 40% ⇒ multiply by 0.60.
• Then increase by 50% ⇒ multiply by 1.50.

Concept / Approach:
Compute sequentially: v1 = 75 * 0.60; then v2 = v1 * 1.50.

Step-by-Step Solution:

Verification / Alternative check:
Net factor = 0.60 * 1.50 = 0.90 ⇒ 75 * 0.90 = 67.5 km/h.

Why Other Options Are Wrong:
60 km/h and 90 km/h incorrectly treat changes as additive or apply them in the wrong order; 60.5 is arbitrary.

Common Pitfalls:
Adding −40% and +50% to get +10% overall; percentage changes compound multiplicatively.

Final Answer:
67.5 km/h