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Percentage question
- Thread starter Pra4ash
- Start date
HallsofIvy
Elite Member
- Joined
- Jan 27, 2012
- Messages
- 7,763
The total number of students is 12+ 3+ 8+ 7+ 9= 39. The "logic" is adding! But in that case the percentage of "students older than 10" is NOT 40%.
Age
7
8
9
10
11
12
# of students
12
3
8
7
9
The percentage of students older than 10 years old is 40%. What is the total number of students?
Hi all! I would like to understand the logic behind the above question. Thank
Pra4ash
But Denis is interpreting the question differently- and probably correctly. Where I interpreted the lack of a number under "11" as meaning there were NO students of age 11, he interpreted it as meaning there is a missing number.
Calling that number "x", there are a total of x+39 students and x+ 9 of them are older than 10. \(\displaystyle \frac{x+ 9}{x+ 39}= .4\). Once you have found x, don't forget that the total number of students is x+ 39.
jashan1985
New member
- Joined
- Aug 1, 2013
- Messages
- 2
Total Number of Students =50
Let number of 11 year old students = x
Total Number of students =12+3+8+7+x+9=39+x
Number of students older than 10 years = x+9
It is given that Number of students who are older than 10 years equals 40% of the total students.
Therefore, we have condition:
((x+9)/(39+x))100=40
When we solve this equation, x comes up equal to 11.
Therefore, total number of students =x+39=11+39=50 students
Age
7
8
9
10
11
12
# of students
12
3
8
7
9
The percentage of students older than 10 years old is 40%. What is the total number of students?
Hi all! I would like to understand the logic behind the above question. Thank
Pra4ash
Let number of 11 year old students = x
Total Number of students =12+3+8+7+x+9=39+x
Number of students older than 10 years = x+9
It is given that Number of students who are older than 10 years equals 40% of the total students.
Therefore, we have condition:
((x+9)/(39+x))100=40
When we solve this equation, x comes up equal to 11.
Therefore, total number of students =x+39=11+39=50 students
Last edited by a moderator:
Let number of 11 year old students = x
Total Number of students =12+3+8+7+x+9=39+x
Number of students older than 10 years = x+9
It is given that Number of students who are older than 10 years equals 40% of the total students.
Therefore, we have condition:
((x+9)/(39+x))100=40
When we solve this equation, x comes up equal to 11.
Therefore, total number of students =x+39=11+39=50 students
Thank you all, I've got it now!
if 12+3+8+7+9 = 60% (0.6), then 40%(0.4) * 12+3+8+7+9/60%(0.6) gives 20.
so, x + 9 = 20
x = 20 - 9
x = 11
Thank you so much again!