The base material for a certain roadbed is 80% crushed rock when measured by weight.
How many tons of this material must be mixed with another material containing 30% crushed rock
to make 150 tons of material that is 40% crushed rock?
Let = tons of 80% material.
This contains tons of crushed rock.
Let = tons of 30% material.
This contains: tons of crushed rock.
The mixture will contain: tons of crushed rock.
But we know that the mixture will be 150 tons which is 40% crushed rock.
. . It will contain: tons of crushed rock.
We just described the final amount of crushed rock in two ways.
There is our equaton! . . .