Answer:
Step-by-step explanation:
Last year
Ratio of the number of middle school students to number of high school students = 1 : 8
Total ratio = 9
Middle school = 1
High school = 8
Total students in the band = x
Middle school = 1/9x
High school = 8/9x
Total = 1/9x + 8/9x
This year
Ratio of the number of middle school students to number of high school students = 2 : 7
Total ratio = 9
Middle school = 2
High school = 7
Total students = x
Middle school = 2/9x
High school = 7/9x
Total = 2/9x + 7/9x
If there are 18 middle school students in the band this year
2/9x = 18
x = 18÷2/9
= 18 × 9/2
= 81
x = 81
Last year:
1/9x + 8/9x
= 1/9 * 81 + 8/9 * 81
= 9 + 72
= 81
This year
2/9x + 7/9x
2/9*81 + 7/9*81
= 18 + 63
=81
Change in middle school =this year - last year
= 18 - 9
= 9 (increase)
Change in high school = this year - last year
= 63 - 72
= -9 (decrease)
