Discussion
What should come in place of the question mark (?) in the given series? 9, 101, 999, 10001, ?
Answer: A
The next number is 99999. The terms are 10 - 1 = 9, 100 + 1 = 101, 1000 - 1 = 999, 10000 + 1 = 10001, so the powers of ten go up by one each time and the added number alternates between -1 and +1. The fifth term is \(10^{5} - 1 = 99999\).
99998 and 99990 break the pattern of a power of ten plus or minus one, and 100000 has the right power but the wrong sign.
Check by the pattern of the differences from powers of ten: 9 is 10 minus 1, 101 is 100 plus 1, 999 is 1000 minus 1 and 10001 is 10000 plus 1. The sign alternates minus, plus, minus, plus, so the next sign is minus and the next power of ten is 100000, which gives 99999.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development