Number series – find the missing term by decreasing differences: 125, 80, 45, ?, 5

Introduction / Context:
This is a simple linear-difference ladder with a steady decrement in the subtractions.

Observation / Approach:

• 125 → 80 (−45)
• 80 → 45 (−35)
• 45 → ? (−25)
• ? → 5 (−15)

Step-by-Step Solution:
Apply the next decrement (−25): 45 − 25 = 20.

Verification / Alternative check:
Continuing: 20 − 15 = 5, which matches the final given term.

Why Other Options Are Wrong:
30, 25, 35, 15 violate the steady “−10 each time” reduction in the subtractions (−45, −35, −25, −15).

Common Pitfalls:
Looking for multiplicative rules where consistent linear decrements suffice.

Final Answer:
20