Foundation
USE WHEN
Price changes while expenditure/budget and quantity consumed are constrained.
BEST METHOD
Equation Method
TARGET
60–90 sec
MASTERY
not started
Price changes while expenditure/budget and quantity consumed are constrained.
Expenditure equals price per unit multiplied by quantity consumed.
If expenditure stays constant and price rises x%, consumption falls by x/(100+x)×100%.
Use P₁Q₁=E₁ and P₂Q₂=E₂, then compare multipliers instead of relying only on shortcut formula.
Timed drill
Identify the base or invariant before you calculate.
Attempt first · Standard Example
Attempt first · CAT-Level Example
3-level practice ladder
Foundation
CAT Standard
Advanced / Hybrid
cat 2020 slot 2: rice and wheat expenditure changes after 20% and 12% price increases.