Can you please help with this percentage-math problem
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Can you please help with this percentage-math problem

[From: ] [author: ] [Date: 12-06-11] [Hit: ]
2 = 50.18 + 28 + (0.35 * 11) = 46 + 3.85 = 49.......
I tried working it out, but I just keep getting the wrong answer!!

Johnny had 3 projects for his english subject, he has completed 2 projects and is yet to complete his third project. Each project has a different weighting and Johnny would like to calculate what mark he needs to achieve in the third project to pass the subject.
NOTE: Assuming a pass equates to 50% of the total marks

Weightings are as follows
Project 1: 25% Johhny recieved: 18/25
Project 2: 40% Johnny recieved: 28/40
Project 3: 35% Johnny recieved: ?????

What mark does Johnny need to achieve in Project 3 in order to pass this unit?


THANKYOUUU

-
Calculate a weighted average of the three grades:

Project 1: 18/25 = 0.72 = 72%

Project 2: 28/40 = 0.7 = 70%

Project 3: x

Average them:

(0.25 * 72) + (0.4 * 70) + (0.35 * x) = 50

Multiply out:

18 + 28 + 0.35x = 50

Subtract 18 and 28 from both sides:

0.35x = 4

Divide both sides by 0.35:

x = 4 / 0.35 = 11.43

He can score as low as 12% and still get a 50% for the course.

Check:

18 + 28 + (0.35 * 12) = 46 + 4.2 = 50.2

18 + 28 + (0.35 * 11) = 46 + 3.85 = 49.85
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