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

Answer: (c)

Using Rule 1,

${x_1+x_2+…x_n}/n$ = $\ov{x}$

∴ $??{i=1}?n $$(x_i - \ov{x})$

= $(x_1 - \ov{x})$+$(x_2 - \ov{x})$+…$(x_n - \ov{x})$

= $({x_1+x_2+…+x_n})$ - n.$\ov{x}$

=n $({x_1+x_2+…+x_n}/n)$ - n.$\ov{x}$

= $n\ov{x} – n\ov{x}$ = 0

Answer: (b)

Temperature on 4th day

= (4 × 25 + 4 × 25.5 –25.2 × 7)°C

= (100 + 102 – 176.4)°C

= 25.6°C

Answer: (b)

Number of students in the class = x (let)

∴ Number of girls = 50 – x

According to the question,

x × 70 + (50 – x) × 75

= 50 × 72

⇒ 70x + 3750 – 75x = 3600

⇒ 3750 – 5x = 3600

⇒ 5x = 3750 – 3600 = 150

⇒ x = $150/5$ = 30

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

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

The required average marks

= ${55×50+60×55+45×60}/{55+60+45}$

= ${2750+3300+2700}/{160}$

= $8750/160$ = 54.68