Due to an increase in 30% in the price of eggs, 3 eggs less are available for Rs. 7.80. Find the present rate of eggs per dozen.

Answer: Option B

Explanation:

Question of this type looks a bit typical, but it is too simple, as below...

It will be 8 * 20/100 = 1.6

Answer: Option A

Explanation:

Actual Price = Rs.25 + Rs.2.50 = Rs.27.5

Saving = Rs.2.5

$$\begin{aligned}\text{Percentage Saving = }\dfrac{2.5}{27.5}\times 100 \\ = \dfrac{250}{27.5} = \dfrac{2500}{275}\\ = \dfrac{100}{11} = 9\dfrac{1}{11}\% \approx 9\%\end{aligned}$$

Answer: Option D

Explanation:

Let their marks be (x+9) and x.
Then, x+9 = 56/100(x + 9 +x)
=> 25(x+9)
=> 14 (2x + 9)
=> 3x = 99
=> x = 33.
So, their marks are 42 and 33

Answer: Option C

Explanation:

Failed in mathematics, n(A) = 34
Failed in English, n(B) = 42
$$\begin{aligned} n(A\cup B) = n(A)+n(B)-n(A\cap B) \\ = 34+42-20 = 56 \\ \text{Failed in either or both subjects are 56} \\ \text{Percentage passed = }(100-56)\% \\ = 44\% \end{aligned}$$

Answer: Option C

Explanation:

Error = (81.5 - 81.472) = 0.028
Required percentage = $$\begin{aligned} \frac{0.028}{81.472} \times 100 = 0.034 % \end{aligned}$$