Find equivalent percent: 30% of 140 equals ?% of 840. Find the missing percent.

Introduction / Context:
This question equates two amounts computed as percentages of different bases. The technique is to compute the left side numerically, then express that value as a percentage of the new base on the right side.

Given Data / Assumptions:
Compute 30% of 140 and set it equal to x% of 840. Solve for x.

Concept / Approach:
Let x be the required percent. Then (x/100)*840 = 0.30*140. Solve for x: x = (0.30*140*100)/840. Simplify to avoid mistakes.

Step-by-Step Solution:

Verification / Alternative check:
Check: 5% of 840 = 0.05 * 840 = 42, matching the left side exactly.

Why Other Options Are Wrong:
15%, 24%, and 60% would give 126, 201.6, and 504 respectively—none equal 42. 3.5% gives 29.4, also incorrect.

Common Pitfalls:
Setting up the equation with reversed bases or forgetting to multiply by 100 when solving for the percent variable.

Final Answer:
5%