Which one is bigger: $\;35{,}043 × 25{,}430\,$ or $\,35{,}430 × 25{,}043\;$? Which of the two quantities is greater?
Quantity A: $\;\;35{,}043 × 25{,}430$
Quantity B: $\;\;35{,}430 × 25{,}043$

What is the best and quickest way to  get the answer without using calculation, I mean using bird's eye view?
If we have two pairs of numbers, and both pairs add up to the same total, then the pair with the larger product will be the pair that's closer together. So the answer is the first pair.

(This picture might help: if you want a rectangle with a fixed perimeter to have the biggest possible area, you want it to be a square.)
Imagine an extreme case of shopping where you have 3 Louis Vuitton bags costing £1,000,000 each. Which is cheaper, getting a discount of £1 per item or putting one bag back? This tells you that 3 x 999,999 is larger than 2 x 1,000,000. And that tells you whether increasing the little term or the big term has a greater effect.