plug-in problem

[Gurpinder]

hey guys,

what am i doing wrong?

the problem is:
at a certain universty, 3 out of every 5 students live in an on-campus dormitory. if one out of every 10 students who do not live in an on-campus dormitory lives in a university owned apartnemtn, what fractional part of the student body does not live in either an on-campus dormitory or a university-owned apartment?

so

let 30 be total number of students

30*3/5 = 18 - so 18 students live on campus dormitory.
30*1/10 = 3 - so 3 students live in a university-owned apartment.

18+3=21.

so 9/30 or 3/10 should be the final answer???? right???? but its not!!!!

please help!

[lkm]

The second step is wrong.

let 50 be total number of students

50*3/5 = 30 - so 30 students live on campus dormitory.
20*1/10 = 2 - so 2 students live in a university-owned apartment.

Remaining students = 18

= 18/50
= 9/25 should be the answer.

[SM2010]

hey guys,

what am i doing wrong?

the problem is:
at a certain universty, 3 out of every 5 students live in an on-campus dormitory. if one out of every 10 students who do not live in an on-campus dormitory lives in a university owned apartnemtn, what fractional part of the student body does not live in either an on-campus dormitory or a university-owned apartment?

so

let 30 be total number of students

30*3/5 = 18 - so 18 students live on campus dormitory.
30*1/10 = 3 - so 3 students live in a university-owned apartment.

18+3=21.

so 9/30 or 3/10 should be the final answer???? right???? but its not!!!!

please help!

I think the answer should be 9/25. (please confirm)

The first line of your working is correct:- 18 students live on campus dormitory (assuming 30 students total).

The second part is incorrect, because the question says "one out of 10 students who do not live in an on-campus dormitory. So in your working you haven't taken this into account. So basically out of all those who DO NOT live in an on-campus dormitory, i.e. 12 (30-18=12), then 1/10 of those live in an apartment.

So the number living in an apartment is:
(1/10)*12= 1.2
Therefore the number of people living in on-campus and apartments is: 18+1.2= 19.2
Therefore number of people not living in either is: 30-19.2=10.8
Therefore fraction is 16.8/30 = 9/25

It would have been easier to stick with fractions in my opinion instead of doing it based on a certain number of people (30 in this case), as you wouldn't get decimal points in the calculations.

[Gurpinder]

ahhhh.....got it....

yes you both are right. the answer is 9/25.

thank you guys.

[frank1]

excatly....
choosing right number is very important
i was trying to do even with out adding 0's to orginal numbers
but that way
1.8/5 was hard to calculate...
so just added 0 to all numbers and after that there was answer in question itself..