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A person has taken four test so far in a class. On the first two test which are worth 20 percent, she got a 69, and a 73. On the third which is worth 25 percent she got an 84. The fourth test is also worth 25 percent, but what grade does that person need for their whole class average to be a 85?

Assume that the last 10 percent is given.

2007-12-11 15:52:12 · 4 answers · asked by smiles 2 in Science & Mathematics Mathematics

4 answers

to find how much each test contritube to the final grade
69x20%=13.8%
73x20%=14.6%
84x25%=21`%
total=49.4%
to achieve final grde of 85% she stillneed 35.6%
but the final test only worth 25% so there is no way she can achieve 85% average

2007-12-11 15:57:34 · answer #1 · answered by someone else 7 · 0 0

I don't quite understand the math that the previous answer is using, but you'd need around a 120 on the final test to get a 85 average.

If we're assuming that the last 10 percent is a 100, (ie a fifth test that is 10% of the grade and she got a 100) that would change the answer.

2007-12-12 00:08:33 · answer #2 · answered by Griffin 1 · 0 0

25x + 25*84 + 20*73 + 20*69 = 90*85
x = (7650 - 1380 - 1460 - 2100) / 25
x = 2710 / 25
x = 108.4%

2007-12-12 00:20:00 · answer #3 · answered by Helmut 7 · 0 0

x = 4th grade to average 85

([0.2{69 + 73}] + [0.25{84] + 0.25x)/(2[0.2] + 2[0.25]) = 85
([0.2{142}] + 21 + 0.25x)/(0.4 + 0.5) = 85
(28.4 + 21 + 0.25x)/0.9 = 85
49.4 + 0.25x = 76.5
0.25x = 27.1
x = 108.4

Answer: she must get a grade of 108.4 which is impossible to attain.

Proof:
= (0.2[69 + 73] + 0.25[84 + 108.4])/0.9
= (0.2[142] + 0.25[192.4])/0.9
= (28.4 + 48.1)/0.9
= 76.5/0.9
= 85

2007-12-12 00:25:12 · answer #4 · answered by Jun Agruda 7 · 3 0

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