Chain rule problems compare two situations where quantities vary directly or inversely. Decide for each quantity whether it increases or decreases the result, then multiply the ratios.
1Variation
Direct proportion: more cost for more items, more work for more men (same time)
Inverse proportion: more men ⇒ fewer days; more hours per day ⇒ fewer days
2Working formula
(M₁ × D₁ × H₁)/W₁ = (M₂ × D₂ × H₂)/W₂