Multiple choice

Find the missing number in the given below series. 20 21 17 26 ? 35

  1. 27

  2. 10

  3. 18

  4. 20

  5. 25
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The series follows an alternating square pattern: +1, -4, +9, -16, +25 (where 1=1², 4=2², 9=3², 16=4², 25=5²). Starting from 20: 20+1=21, 21-4=17, 17+9=26, 26-16=10, 10+25=35. The missing number is 10. Options like 27 and 25 might seem plausible through simple arithmetic patterns, but only 10 satisfies the alternating square sequence.

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