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Averages for CAT: Formulas, Weightage & Question Types

Two groups combined, someone joining or leaving, and squeezing one value to its limit.

Averages formula sheet

Everything CAT needs from Averages, in one place. Bookmark it for revision; the lesson in the app explains where each line comes from and when to reach for it.

Everything for this chapter, in one place. nn is the count and AA the average.

The only definition

AverageA=sumnA = \dfrac{\text{sum}}{n}
The form you will actually usesum=average×count\text{sum} = \text{average} \times \text{count}
Deviationsthe gaps above AA and the gaps below AA cancel exactly

Adding or removing one value

Add a value vv to nn itemsnew average =nA+vn+1= \dfrac{nA+v}{n+1}
The shiftv−An+1\dfrac{v-A}{n+1} — so the average rises if and only if v>Av > A
Remove a value vvnew average =nA−vn−1= \dfrac{nA-v}{n-1}
Replace vv with wwthe total moves by w−vw-v, the average by w−vn\dfrac{w-v}{n}

Two groups combined

Weighted averageA=n1A1+n2A2n1+n2A = \dfrac{n_1A_1 + n_2A_2}{n_1+n_2}
Alligationn1n2=A2−AA−A1\dfrac{n_1}{n_2} = \dfrac{A_2 - A}{A - A_1}
In wordsthe combined average sits closer to the bigger group

Shifting and scaling

Add kk to every valuethe average goes up by kk
Multiply every value by kkthe average is multiplied by kk
Assumed meanA=guess+average of the deviations from the guessA = \text{guess} + \text{average of the deviations from the guess}

Evenly spaced values

Average of an APfirst+last2\dfrac{\text{first}+\text{last}}{2}, which is the middle term
First nn natural numbersn+12\dfrac{n+1}{2}
nn consecutive integersthe middle one when nn is odd

Averages that are not plain averages

Average speedtotal distancetotal time\dfrac{\text{total distance}}{\text{total time}} — never the average of the speeds
Equal distances at two speedsthe harmonic mean 2xyx+y\dfrac{2xy}{x+y}
Equal money spent at different ratesthe average rate is the harmonic mean, not the arithmetic one
Equal quantity bought at different ratesthen it is the arithmetic mean

The 5 Averages question types CAT repeats

Past CAT papers return to the same few shapes. Learn to recognise them and most questions become a known routine. Beyond these, CAT has asked 3 rarer one-off shapes here.

  1. 01

    Squeeze one value to its limit

  2. 02

    Two groups, one combined average

  3. 03

    Relations between sums

  4. 04

    Overlapping groups — first kk and last kk

  5. 05

    Someone joins, leaves or is replaced

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Averages in CAT: quick answers

How many Averages questions come in CAT Quant?
About 1.3 questions in a 22-question Quant section, worth roughly 4 marks. Averages appeared in 23 of the 24 CAT papers from 2017 to 2025, 32 questions in all, which ranks it 5 of 25 Quant chapters.
Are Averages questions in CAT MCQ or TITA?
38% of the Averages questions asked since 2017 were TITA (type in the answer, no negative marking). The rest were multiple choice.
What types of Averages questions does CAT ask?
CAT keeps returning to 5 question shapes in Averages: Squeeze one value to its limit; Two groups, one combined average; Relations between sums; Overlapping groups — first k and last k; Someone joins, leaves or is replaced.

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