30 is 20% of 150 i.e. 20% of total 150 students in the marching bank play the trumpet.
Step-by-step explanation:
Draw two number lines:
One number line to represent number of students from 0 to 150. For convenience, divide the number line into intervals of 15 so that 30 is also present on the line.
Second number line to represent percentage and divide it in intervals from 1 to 100.
Now, place the other number line just below the other number line and draw a vertical line as shown the attached figure.
We find out that 30 is at 20% of 150.
It means that 20% (30 of total 150) of total 150 students in the marching band, play trumpet.