can you help me with a gr.7 math question?

Question

here's the question:
a teacher records the test marks of 25 students and calculates the class mean to be 72. jean-pierre finds out that his mark of 86 was recorded incorrectly as 36. what will the corrected class mean be?
i checked the answer key and it says the new class mean is 74, but i dont get how they got 74, so can you show me how you got 74, or you can show me how you did it and what you get so i'll know what went wrong and how i should do it. thank you!!! (and by the way, if you dont know what i'm talking about, then get lost)

Answer 1

Jean-Pierre's new mark would raise the total of class marks by 50 marks (86-36=50). Divide 50 by the number of students 25 and you get 2. So 2 marks are added to the class mean of 72 to get 74.

Answer 2

you multiply 25 with 72 = 1800
take it back a step. you add all the grades together and then devide by the number of students. right? thats how you get a mean. so go backwords. multiply what you have to see what all the grades add up to. like an equation....
x/25=72
72 *25= x


add 50 (86-36) to 1800= 1850
try to correct the grade. subtract the 36 from the sum of all the grades and add 86.

devide back by 25 = 74
now that you have the right sum, just devide it by the number of students to get the mean.


=]

hope it helped