An 80 g ornamental gold chain contains 40% gold, what is the amount of gold required by the goldsmith to make 30 such chains? Express your answer in kilograms.

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Hint: In this question, it is given that an 80 g ornamental gold chain contains 40% gold. So at first we have to find the amount of gold in this chain and then have to find how much we need to make 30 such chains.

Given,
An 80 g ornamental gold chain contains 40% gold.
Here, we will first change the percentage into amount of gold in one chain:
[Percent means per 100, it means if we have 100 g ornamental and it contains 40 g of gold]
So, total gold in one chain = $80 \times \dfrac{{40}}{{100}}$g = 32 g
Therefore, in one gold chain there is 32 g of gold.
Using unitary method,
To make 30 such chains the amount of gold required by goldsmith is = $30 \times 32 = 960$g
Now, to express the amount of gold obtained in kilogram:
We know, 1 kg = 1000 g
So, 1 g = 0.001 kg
960 g = 0.001 × 960 kg = 0.96 kg
The amount of gold required by the goldsmith to make 30 such chains is 0.96 kg.

Note: In these types of questions, two concepts are applied: (1) Percentage and (2) Unit conversion. To solve this problem we have to know how to change the percentage value into a particular thing, and then we can find the amount of gold on the chain. We should have knowledge of the unitary method for finding the amount for more than one chain. Also we should have knowledge of unit conversion.