Question

Given that the weight of $12$ sheets of thick paper is $40$ grams. How many sheets of the same paper would weigh $2\frac{1}{2}$ kilograms?
[3 marks]

Answer 1

Let the number of sheets which weigh $2\frac{1}{2}$ kg be $x$.

$\because 1kg=1000grams$
$\Rightarrow \frac{5}{2}kg=\frac{5\times 1000}{2}grams=2500grams$

Number of sheets	$12$	$x$
Weight of sheets (in grams)	$40$	$2500$

[1 mark]

More the number of sheets, the more would their
weight be. So, the number of sheets [N] and their weights [W] are directly proportional to each other.

$\Rightarrow \frac{N}{W}=constant$
$\Rightarrow \frac{N_1}{W_1}=\frac{N_2}{W_2}$

[1 mark]

$\Rightarrow \frac{12}{40}$ = $\frac{x}{2500}$
$\Rightarrow x=\frac{12\times 2500}{40}=750$ sheets

Thus, the required number of sheets of paper is $750$.

[1 mark]