Certificates / Quantitative aptitude / Number Series
Number Series: lesson, then the certificate test
Step 1: the lesson (about 1 min)
Find the rule that turns each number into the next, then apply it once more.
- Check the differences; if they are not equal, check the differences of the differences.
- Check ratios (× 2, × 3), squares and cubes (n², n³ ± 1), and "× a + b" rules.
- If nothing fits, the series may be two series alternating: check every second term.
Worked example
3, 7, 15, 31, 63, ?
- 7 = 3 × 2 + 1, 15 = 7 × 2 + 1, 31 = 15 × 2 + 1, 63 = 31 × 2 + 1
- Next: 63 × 2 + 1 = 127
Answer: 127
Watch out
- Stopping at the first pattern that fits two terms: check it against every term.
Made by Shishya (AI-assisted): a general method in our own words, with our own example; no exam or platform question is copied.
Step 2: the test
- 15 questions from Shishya's checked question bank, 20 minutes. Pass mark: 11 correct.
- Scored on Shishya's server; the answers are not shown afterwards, so the test stays fair. Each attempt draws new questions.
- Free. Your first test needs no account; sign up free to take more. Your answers and score are not stored; if you pass, you choose the name to print (ages 13 and up).
- It is a Shishya completion certificate — not a university or government credential. The test is not supervised.