* Let 'b' represent the number of boys in the band.
* Let 'g' represent the number of girls in the band.
We know:
* g = 3b (There are 3 times as many girls as boys)
* b + g = 100 (The total number of students is 100)
Now we can solve for 'b' and 'g':
Substitute the first equation (g = 3b) into the second equation:
b + 3b = 100
Combine like terms:
4b = 100
Divide both sides by 4:
b = 25
Now substitute the value of 'b' back into either equation to find 'g'. Let's use the first equation:
g = 3b = 3 * 25 = 75
Therefore, there are $\boxed{25}$ boys and $\boxed{75}$ girls in the marching band.