In expressing a length of 81.472 km as nearly as possible with the three significant digits, find the percentage error

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:

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

Answer: Option B

Explanation:

Clearly,
x% of 150 = 150 - x [as x is number of boys]

\begin{aligned}
=> x + \frac{x}{100} * 150 = 150 \\

=> \frac{5}{2}x = 150 \\

=> x = 60 \\
\end{aligned}

Answer: Option B

Explanation:

It will 20*1/100 = 1/5

Answer: Option D

Explanation:

It will be 1/2(1%) = 1/2(1/100) = 1/200 = 0.005