model 5 find new average from error Practice Questions Answers Test with Solutions & More Shortcuts

average PRACTICE TEST [9 - EXERCISES]

model 1 basic average questions

model 2 average of consecutive numbers

model 3 twice, thrice, one third etc. of numbers

model 4 find nth average from 1st & last number

model 5 find new average from error

model 6 find average of excluded number

model 7 average on ages/weight

model 8 find monthly income

model 9 average on cricket/exam

average Important Formulas, Rules, Concepts & Shortcuts

Question : 41 [SSC CGL Tier-I 2015]

The average marks obtained by a student in 6 subjects is 88. On subsequent verification it was found that the marks obtained by him in a subject was wrongly copied as 86 instead of 68. The correct average of the marks obtained by him is

a) 85

b) 87

c) 86

d) 84

Shortcut »

Answer: (a)

Correct sum of marks obtained by the student

= 88 × 6 – 86 + 68

= 528 – 86 + 68 = 510

∴ Correct average = $510/6$ = 85

Aliter : Using Rule 26,

The correct average will be = m +${\text"(a-b)"}/ \text"n"$.

Here, n = 6, m = 88

a = 68, b = 86

Correct mean = m + ${\text"(a - b)"}/\text"n"$

= 88 +${(68 - 86)}/6$

= 88 - $18/6$ = 85

Question : 42 [SSC CHSL 2010]

While finding the average of 10 given numbers, a student, by mistake, wrote 64 in place of a number 46 and got his correct average 50. The correct average of the given numbers is :

a) 48.3

b) 48.2

c) 49.3

d) 49.1

Shortcut »

Answer: (b)

Difference of numbers = 64 – 46 = 18

Correct average = 50 – $18/10$ = 50 – 1.8 = 48.2

Aliter : Using Rule 26,

The correct average will be = m +${\text"(a-b)"}/ \text"n"$.

Here, n = 10, m = 50

a = 46, b = 64

Correct Average = m + ${\text"(a - b)"}/\text"n"$

= 50 + ${(46 – 64)}/10$

= 50 -$18/10$

= 50 – 1.8 = 48.2

IMPORTANT quantitative aptitude EXERCISES

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