List of top Quantitative Aptitude Questions on Sequence and series asked in CAT

The average of a non-decreasing sequence of N numbers \(a_1,a_2,…,a_N\) is 300.If \(a_1\) is replaced by \(6a_1\), the new average becomes 400.Then,the number of possible values of \(a_1\) is
The average of all 3-digit terms in the arithmetic progression 38,55,72,...,is

A and B can complete a task in 12 days, B and C in 15 days, and A and C in 20 days. How many days will A alone take?