Mean, Third and Fourth Proportional Questions with Solutions

These three question types all ask you to complete a proportion with a missing term — the only real skill is setting up the right proportion statement before cross-multiplying. Here’s the concept, four fully worked examples, and a few to try yourself.

The concept, quickly

• Fourth proportional to a, b, c: find x such that a : b = c : x. Cross-multiplying gives x = (b × c) / a.
• Third proportional to a, b: find x such that a : b = b : x — note b is repeated. Cross-multiplying gives x = b² / a.
• Mean proportional between a and b: find x such that a : x = x : b — x is repeated this time. Cross-multiplying gives x² = a × b, so x = √(ab).
• The three are easy to mix up because they all involve three given-or-implied numbers — write out the proportion statement explicitly first, with the unknown in its correct position, before cross-multiplying.

Worked examples

Try these yourself

Write out the proportion statement first, then cross-multiply, and check against the answer.

Where this comes up

Mean, Third and Fourth Proportional is a regular sub-topic within the Quantitative/Numerical Aptitude section of every exam Pariksha Saathi covers — SSC CGL, SSC MTS, SSC CHSL, IBPS PO, IBPS Clerk, SBI PO and SBI Clerk — building directly on Ratio and Proportion.

Practice more Mean, Third and Fourth Proportional questions

This page covers the concept and a handful of worked examples. Pariksha Saathi has full topic-wise practice sets for Mean, Third and Fourth Proportional (and every other Quant/Reasoning/English topic) with instant scoring and explanations — free, no account required.