The correct option is
A 1 kg 925 g
Weight of Rock 1 = 1 kg 450 g
Weight of Rock 2 = 4 kg 325 g
Total weight of the three rocks = 7 kg 700 g
∴ Weight of Rock 3 can be written as:
![](https://df0b18phdhzpx.cloudfront.net/ckeditor_assets/pictures/1206186/original_Screenshot_2021-06-27_at_7.58.02_AM.png)
To calculate the weights of Rock 1 and Rock 2, we calculate the sum of 1 kg 450 g and 4 kg 325 g.
Converting the weights from kilograms to grams, we get:
![](https://df0b18phdhzpx.cloudfront.net/ckeditor_assets/pictures/1206648/original_Screenshot_2021-06-27_at_1.41.43_PM.png)
So, (1 kg 450 g + 4 kg 325 g) can be calculated as (1450 g + 4325 g).
Calculating 1450 + 4325 using the standard method, we get:
![](https://df0b18phdhzpx.cloudfront.net/ckeditor_assets/pictures/1206184/original_Screenshot_2021-06-27_at_7.56.38_AM.png)
∴ The total weight of Rock 1 and Rock 2 is 5775 g.
Hence, we can see:
![](https://df0b18phdhzpx.cloudfront.net/ckeditor_assets/pictures/1206187/original_Screenshot_2021-06-27_at_7.59.24_AM.png)
Calculating 7700 - 5775 using the standard method, we get:
![](https://df0b18phdhzpx.cloudfront.net/ckeditor_assets/pictures/1206188/original_Screenshot_2021-06-27_at_8.00.03_AM.png)
∴ The weight of Rock 3 = 1925 g
= 1 kg 925 g