Mixture and Alligation

The alligation cross method — a shortcut for finding the ratio to mix two ingredients at different prices or concentrations.

📖 ~4 min read 📐 RRB NTPC / Group D — Mathematics

For cheaper price C and dearer price D, mixed to give mean price M:
Ratio (Cheaper : Dearer) = (D − M) : (M − C)

💡 Example: Tea at ₹60/kg mixed with tea at ₹90/kg to get a mixture at ₹75/kg. Ratio = (90−75):(75−60) = 15:15 = 1:1

If x units are withdrawn from y units of pure liquid and replaced with water, repeated n times:
Final quantity of liquid = y × (1 − x/y)ⁿ

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