Question
CSATMediumPrelims 2016Maths

Two numbers X and Y are respectively 20% and 28% less than a third number Z. By what percentage is the number Y less than the numbers X?

Explanation

Let the third number be Z.

X is 20% less than Z: X=Z(120%)=Z0.80X = Z \cdot (1 - 20\%) = Z \cdot 0.80 Y is 28% less than Z: Y=Z(128%)=Z0.72Y = Z \cdot (1 - 28\%) = Z \cdot 0.72 To find the percentage by which Y is less than X, use the formula: Percentage decrease = ((XY)/X)100 ((X - Y) / X) \cdot 100

Substituting values of X and Y: Percentage decrease = ((0.80Z0.72Z)/(0.80Z))100 ((0.80 \cdot Z - 0.72 \cdot Z) / (0.80 \cdot Z)) \cdot 100 Percentage decrease = ((0.08Z)/(0.80Z))100 ((0.08 \cdot Z) / (0.80 \cdot Z)) \cdot 100 Percentage decrease = 0.101000.10 \cdot 100 Percentage decrease = 10%

Maths PYQs from 2016

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