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

Answer: (d)

That month will have 5 sundays.

∴ Required average

= ${5×510+25×240}/30$

= ${2550+6000}/30$

= $8550/30$ = 285

Aliter : Using Rule 10,

Here, $n_1$ = 5, $a_1$ = 510

$n_2$ = 25, $a_2$ = 240

Answer: (b)

Using Rule 10,

If the average of '$n_1$' numbers is $a_1$ and the average of '$n_2$' numbers is $a_2$, then average of total numbers $n_1$ and $n_2$ is

$Average = {n_1a_1 + n_2a_2}/{n_1 + n_2}$

Required average weight

$(50×6+51×2+55×2)/10$

= ${300+102+110}/10$ = $512/10$

= 51.2 kg

Answer: (a)

Male employees = x

Female employees = y

∴ (x + y) 12000 = x × 15000 + y × 8000

⇒ (x + y) × 12 = 15x + 8y

⇒ 12x + 12y = 15x + 8y

⇒ 3x = 4y

⇒ $x/y$ = $4/3$ ⇒ x : y = 4 : 3

Answer: (d)

Using Rule 10,

If the average of '$n_1$' numbers is $a_1$ and the average of '$n_2$' numbers is $a_2$, then average of total numbers $n_1$ and $n_2$ is

$Average = {n_1a_1 + n_2a_2}/{n_1 + n_2}$

Students in class A ⇒ x

Students in class B ⇒ y

Students in class C ⇒ z

For classes A and B,

${83x + 76y}/{x+y}$ = 79

⇒ 83x + 76y = 79x + 79y

⇒ 83x – 79x = 79y – 76y

⇒ 4x = 3y

For classes B and C

${76y+85z}/{y+z}$= 81

⇒ 76y + 85z = 81y + 81z

⇒ 5y = 4z

∴ 20x = 15y = 12z

⇒ ${20x}/60$ = ${15y}/60$ = ${12z}/60$

⇒ $x/3$ = $y/4$ = $z/5$

∴ Required average

${83×3+76×4+85×5}/{3+4+5}$

${249+304+425}/12$ = $978/12$

= 81.5

Answer: (c)

Difference = 83 – 53 = 30

Incorrect observation > Correct observation

∴ Required average

= 35 - $30/100$ = 35 – 0.3 = 34.7

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