model 1 basic average questions Section-Wise Topic Notes With Detailed Explanation And Example Questions

Answer: (b)

Let the last number be x.

According to the question,

18 × 10 + 11 × 20 + x = 30 × 15

⇒ 180 + 220 + x = 450

⇒ 400 +x = 450

⇒ x = 450 – 400 = 50

Answer: (c)

Using Rule 1,

Average of two or more numbers/quantities is called the mean of these numbers, which is given by

$\text"Average(A)" = \text"Sumof observation / quantities"/\text"No of observation / quantities"$

∴ S = A × n

Mean = ${3 +11+ 9+7+15+ 13+ 8 +19 +17 +21 +14+x}/12$

According to question,

${137+x}/12$ = 12

∴ 137 + x = 144

∴ x = 144 – 137 = 7

Answer: (c)

Difference = 83 – 53 = 30

Incorrect observation > Correct observation

∴ Required average

= 35 - $30/100$ = 35 – 0.3 = 34.7

Answer: (d)

If the average of remaining numbers be x, then

20 × 15 = 5 × 12 + 15x

⇒ 300 = 60 + 15x

⇒ 15x = 300 – 60 = 240

⇒ x = $240/15$ = 16

Aliter : Using Rule 13,

Here, m = 20, x = 15

n = 5, y = 12

Average of remaining Numbers = $({mx-ny}/{m-n})$

= $({20×15-5×12}/{20-5})$

= $({300-60}/15)$ = $240/15$ = 16

Answer: (c)

Required average

${32×60+33×40}/72$

${1920+1320}/72$ = $3240/72$ = 45

Answer: (c)

Weight of new person

= (65 + 8 × 2.5) kg

= (65 + 20) kg

= 85 kg

Aliter : Using Rule 23,

Here, x = 2.5, n = 8

Weight of new person

= weight of replaced boy + x × n