Question 718456
You get a mark of 80% on the first test, and the average of the marks of the first two tests is 15% higher than the mark on the last one.
 The average of all marks is 70%. What are the marks of all three tests.
:
Looking at your answer, I noticed that 75 is not 15% more than 60, anyway
:
Let x = the mark on the third test
then
"the average of the marks of the first two tests is 15% higher than the mark on the last one"
2(1.15x) = total marks on the 1st two tests
:
{{{(2(1.15x) + x)/3}}} = 70
2.30x + x = 3(70)
3.30x = 210
x = 210/3.3
x = 63.64, his grade on the third test
:
Then
1.15(63.64) = 73.18 is the average on the 1st two test
:
Find the mark on the 2nd test, call it y:
{{{(80+y)/2}}} = 73.18
80+y = 2(73.18)
y = 146.36 - 80
y = 66.36 is the grade on the 2nd test
:
 What are the marks of all three tests. 80, 66.36, 63.64
:
See if this works out
av = {{{(80 + 66.36 + 63.64)/3}}}
av = {{{210/3}}} = 70 
and find 15% more than the 3rd grade
1.15(63.64) = 73.2 which is the average of 80 and 66.36