Jawabanmu

2013-12-18T00:09:31+07:00
Mean = 4x20 + 5x40 + 6x70 + 8a + 10x10
6 = (80 + 200 + 420 + 8a +100)/140+a
6 (140 + a) = 800 + 8a
840 + 6a = 800 + 8a
2a = 40
a = 20