Question 168105
test 1 = 25% have 76%
test 2 = 25% have 77%
test 3 = 30% have x%
.
.25(76) + .25(77) + .30(x) >= 75
19 + 19.25 + .30(x) >= 75
38.25 + .30(x) >= 75
.30(x) >= 36.75
x >= 36.75/.30
x >= 122.5
.
This says you need to score 122.5% on test 3.  
Which is impossible unless you can score "extra credit".