5:15 Stratified Sampling - Corbettmaths
Corbettmaths clearly explains how to work out a stratified sample, ideal for GCSE.
Stratified samples
Understand how to take a stratified sample
4 hand-picked video lessons for this topic, each checked for relevance and clarity, graded by difficulty and labelled by depth. Press play to watch — nothing loads from YouTube until you do.
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4 shown 5:15 
4:27 Stratified Sampling
Maths Genie walks through a full stratified sampling exam question step by step.
6:41 How to use stratified sampling
3minutemaths tackles a real grade 5 GCSE stratified sampling question by year and gender.
3:49 A-Level Maths: K1-07 [Sampling Methods: Stratified Sampling]
TLMaths explains stratified sampling proportions clearly, transferable straight to GCSE questions.