The ratio given for cement to sand to gravel is 1 : 3 : 4, and all these make concrete.
Add all the numbers in the ratio:
[tex]1+3+4=8[/tex]
Divide the amount of concrete by this number:
[tex]480\text{ kg} \div8=60\text{ kg}[/tex]
This means that each unit in the ratio represents 60 kg when there is a total of 480 kg of concrete. Now let's look at the given ratio again:
[tex]1:3:4[/tex]
The middle number, 3, represents the amount of sand. Multiply this with 60 kg to get the amount of sand needed.
[tex]3 \times 60 \text{ kg} = 180 \text{ kg}[/tex]
180 kilograms of sand are needed. Let me know if you need any clarifications, thanks! (◕‿◕)
~ Padoru
