Approximation and quick calculation: Evaluate (421 × 0.9) + (130 × 101) + 10000 and select the closest option.

Difficulty: Easy

Correct Answer: 23500

Explanation:


Introduction / Context:
This blends a small decimal scaling with an easy product and a large constant. Compute each piece separately, then sum. Option spacing (thousands) allows a quick precise pick without heavy computation.


Given Data / Assumptions:

  • 421 * 0.9
  • 130 * 101
  • + 10000


Concept / Approach:
Use 0.9 = 1 − 0.1 to scale down 421 quickly, multiply 130*101 using 130*(100+1), then add 10000. This keeps the arithmetic mental and exact to the unit place if desired.


Step-by-Step Solution:

421 * 0.9 = 421 − 42.1 = 378.9 130 * 101 = 13000 + 130 = 13130 Sum = 378.9 + 13130 + 10000 = 23508.9 Closest option: 23500


Verification / Alternative check:
Rounding 378.9 to 379 gives 23509; still nearest to 23500 compared to 24500 or 33500.


Why Other Options Are Wrong:
33500 and 24500 deviate by thousands; 225000 is two orders of magnitude too large.


Common Pitfalls:
Multiplying 130*101 as 130*100 only and forgetting the additional 130; or treating 0.9 as 1.0 inadvertently, adding an extra ~42 to the sum.


Final Answer:
23500

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