Respuesta :
Answer:
Step-by-step explanation:
Well, he completed 12 questions, so he has 18 left.
To get the solution, we are looking for, we need to point out what we know:
We assume, that the number 30 is 100% - because it's the output value of the task.
We assume, that x is the value we are looking for.
If 30 is 100%, so we can write it down as 30=100%.
We know, that x is 40% of the output value, so we can write it down as x=40%.
Now we have two equations:
1) 30=100%
2) x=40%
where left sides of both of them have the same units, and both right sides have the same units, so we can do something like that:
30/x=100%/40%
Now we just have to solve the equation.
30/x=100/40
(30/x)*x=(100/40)*x - we multiply both sides of the equation by x
30=2.5*x - we divide both sides of the equation by (2.5) to get x
30/2.5=x
12=x
x=12
now we have:
40% of 30=12
Then, you need to subtract 12 from 30 to figure out what is left.
