Suppose that 6% of the eighth graders and 3% of the seventh graders at Washington Junior High participate in MATHCOUNTS. There are 2 times as many 8th graders as 7th graders at the school. What percentage of the 7th and 8th graders, taken together, participate i
Let N be the number of seventh-graders.....then, 1.5N = the number of eigth--graders....so we have
[.06(1.5)N + .03(N)] / [N + 1.5N] =
[.09N + .03N] / [ 2.5N] =
[.12N] / [2.5N] = ["cancel" the "N's" ]
.12/2.5 = .048 = 4.8%
+36916 N = 7th graders
2N = 8th graders
[.06 (2N) + .03(N) ] / 3N = [.12 +.03]/3 = .05 = 5% of total students
