Ok, so based on a survey - you know that out of 30 students, 11 said that their favourite subject is mathematics. :-)
This means that:
11/30 of these students think mathematics if their favourite subject.
Now, in order to answer your question, we are going to have to change the denominator of the fraction above to 1000. Whatever we do to the denominator of this fraction, we must do to the numerator of this fraction.
Example:
This means that rounded to the nearest ten, theoretically speaking, 370 students out of 1000 would say that mathematics is their favourite subject.
This means that:
11/30 of these students think mathematics if their favourite subject.
Now, in order to answer your question, we are going to have to change the denominator of the fraction above to 1000. Whatever we do to the denominator of this fraction, we must do to the numerator of this fraction.
Example:
This means that rounded to the nearest ten, theoretically speaking, 370 students out of 1000 would say that mathematics is their favourite subject.