Question

Fill in the missing number:
5, 13, 25, 41, ?, 85, 113, 145

• A. 42
• B. 64
• C. 63
• D. 61
• E. None of the above

Answer 1

The correct option is D 61

13 = 5 + 4 $\times$ 2, 25 = 13 + 4 $\times$ 3, 41 = 25 + 4 $\times$ 4 ? = 41 + 4 $\times$ 5, 85 = ? + 4 $\times$ 6
113 = 85 + 4 $\times$ 7, 145 = 113 + 4 $\times$ 8
$\therefore$ ? = 41 $\times$ 4 $\times$ 5 = 61. With this choice, 85 = ? + 4 $\times$ 6
= 61 + 24, which follows the pattern.