GATE CS - GENERAL APTITUDE:Quantitative Ability

Mastering quantitative ability concepts and implementation.

Quantitative Ability for GATE GA

Quant GA is school-level arithmetic under time pressure. Formulas help; units and percentages of what matter more.

Topic	Remember
Percentages	$x\%$ of $A = (x/100)A$; successive % changes are not additive
Ratio/proportion	$a:b = c:d \Rightarrow ad=bc$
Average	Sum / n; combined average = weighted
Time–work	Rate = 1/time; together add rates
Speed–distance	$v = d/t$; average speed ≠ arithmetic mean of speeds unless same time
Simple interest	$SI = Prt/100$
Compound (light)	$A = P(1+r/100)^n$ when asked

Price up 20% then down 20%: net factor $1.2 \times 0.8 = 0.96$ → 4% down, not back to start.

Equal distances at 40 and 60: harmonic mean $2ab/(a+b) = 48$ , not 50.

Tables/bar charts: read axis units first. Prefer computing one cell carefully over estimating all.

$P(n,r) = n!/(n-r)!$ , $C(n,r) = n!/(r!(n-r)!)$ . GATE GA rarely goes deep — watch for "arrangements in a line vs circle" distractors.

Progress

Topic	Remember
Percentages	\(x\%\) of \(A = (x/100)A\); successive % changes are not additive
Ratio/proportion	\(a:b = c:d \Rightarrow ad=bc\)
Average	Sum / n; combined average = weighted
Time–work	Rate = 1/time; together add rates
Speed–distance	\(v = d/t\); average speed ≠ arithmetic mean of speeds unless same time
Simple interest	\(SI = Prt/100\)
Compound (light)	\(A = P(1+r/100)^n\) when asked