Question Detail

Find the sum of first 30 natural numbers

Answer: Option C

Explanation:

Sum of n natural numbers
$\begin{aligned} = \frac{n(n+1)}{2} \end{aligned}$

$\begin{aligned} = \frac{30(30+1)}{2} = \frac{30(31)}{2} = 465 \end{aligned}$

1. Find the average of all numbers between 6 and 34 which are divisible by 5

Answer: Option B

Explanation:

$\begin{aligned} Average = (\frac{10+15+20+25+30}{5}) = \frac{100}{5} =20 \end{aligned}$

2. A batsman makes a score of 87 runs in the 17th match and thus increases his average by 3. Find his average after 17th match

Answer: Option D

Explanation:

Let the average after 17th match is x
then the average before 17th match is x-3

so 16(x-3) + 87 = 17x
=> x = 87 - 48 = 39

3. Average of first five multiples of 3 is

Answer: Option A

Explanation:

$\begin{aligned} Average = \frac{3(1+2+3+4+5)}{5} = \frac{45}{5} = 9 \end{aligned}$

4. Average of 10 matches is 32, How many runs one should should score to increase his average by 4 runs.

Answer: Option B

Explanation:

Average after 11 innings should be 36

So, Required score = (11 * 36) - (10 * 32)
= 396 - 320 = 76

5. A library has an average of 510 visitors on Sundays and 240 on other day. The average number of visitors in a month of 30 days starting with sunday is

Answer: Option B

Explanation:

As the month begin with sunday, so there will be five sundays in the month. So result will be:
$\begin{aligned} = (\frac{510 \times 5 + 240 \times 25}{30}) = (\frac{8550}{30}) = 285 \end{aligned}$