Fraction series
Number Theory
Level
3
Find the missing number in this series: 3, 5/3, 7/5, 11/7, ? 17/11
If the answer can be expressed as a/b, find a+b.
You can try this or My Other Problems .
The answer is 22.
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The series can be expressed as 3/1, 5/3, 7/5, 11/7, a/b, 17/11. Now if we look at the numerators,it's the series of ascending prime numbers: 3,5,7,11,.. while the denominators represent the series of ascending odd numbers: 1,3,5,7.... So a must be = 13 (prime after 11) & b = 9 (odd after 7). Thus, a + b = 1 3 + 9 = 2 2