Question

# A pencil box weighs $225g$. How much do eight such pencil boxes weigh?

Hint: Use a unitary method to calculate the weight of eight boxes, which determines the value of multiple objects based on the data about the single object. As each box weighs $225g$, multiply $225g$ by $8$ to calculate the weight of all such pencil boxes.

We know that the weight of a pencil box is $225g$. We have to calculate the total weight of eight such pencil boxes.
To do so, we will multiply the weight of each pencil box by the total number of pencil boxes.
Thus, we have weight of eight pencil boxes $=225g\times 8=1800g$.
The weight of eight pencil boxes is $1800g$.
We can convert this weight to kilograms as well.
We know that $1kg=1000g$. Thus, we have $1g=\dfrac{1}{1000}kg$.
To convert $x$ grams into kilograms, we will multiply $x$ by $\dfrac{1}{1000}$.
Substituting $x=1800$, we have $1800g=1800\times \dfrac{1}{1000}=1.8kg$.
Thus, we have $1800g=1.8kg$.
Hence, the weight of eight pencil boxes is $1800g$ or $1.8kg$.

Note: Unitary method is a technique used for solving a problem by first finding the value of a single unit and then finding the necessary value by multiplying the single unit value. The word unitary refers to a single or individual unit. Hence, this method aims at determining the value in relation to a single unit. Kilograms and grams represent units of measurement of weight. The International System of Units takes Newton as the unit of measurement of weight. We can always convert from one unit of measurement to another one using the unitary method. While performing calculations, one should be careful about the units of weight. Otherwise, we will get an incorrect answer.