Multiple choice

In the following number series, one number is wrong. Find that wrong number. 12, 16, 23, 50, 99, 220, 389

  1. 16

  2. 23

  3. 50

  4. 99

  5. 220

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The series is 12, 16, 23, 50, 99, 220, 389. Pattern: +4, +7, +27, +49, +121, +169. The additions are squares: 4=2², 7(not a square), 27(not a square), 49=7², 121=11², 169=13². Better pattern: differences of differences: 7-4=3, 27-7=20, 49-27=22, 121-49=72... not clean. Try: 12+4=16, 16+7=23, 23+27=50, 50+49=99, 99+121=220, 220+169=389. The additions 4, 7, 27, 49, 121, 169 - prime squares except 7 and 27. If pattern was 2², 3², 5², 7², 11², 13² = 4, 9, 25, 49, 121, 169 then: 12+4=16, 16+9=25 (not 23), 25+25=50, 50+49=99, etc. So 23 is wrong.