CAT (QA) PYQs

A CAT aspirant appears for a certain number of tests. His average score increases by $1$ if the first $10$ tests are not considered, and decreases by $1$ if the last $10$ tests are not considered. If his average scores for the first $10$ and the last $10$ tests are $20$ and 30, respectively, then the total number of tests taken by him is

In a group of $10$ students, the mean of the lowest $9$ scores is $42$ while the mean of the highest $9$ scores is $47$. For the entire group of $10$ students, the maximum possible mean exceeds the minimum possible mean by

The average weight of students in a class increases by $600$ gm when some new students join the class. If the average weight of the new students is $3$ kg more than the average weight of the original students, then the ratio of the number of original students to the number of new students is