the average of 9 observations was 9 , that of the 1 st of 4 being 10 and that of the last 4 being 8 . what was the 5 th observation ?
"1 to 9 = 9 * 9 = 81 1 to 4 = 4 * 10 = 40 4 to 9 = 6 * 8 = 48 5 th = 48 + 40 = 88 – 81 = 7 answer : d"
subtract(add(multiply(10, 4), multiply(9, 4)), multiply(9, 9))