1. Evaluate (101.5)? - (100.5)

Roughly 18,000

Step-by-step explanation:

When you need to do rough mental math, you can do something like 720 vs 25 or 30 which is pretty simple to do in your head.

If you are very proficient in mental math, you can do something like 720 * 25, which is harder, but if you know the tricks, you can do this quickly.

720 * 25

Multiply 25 by 7.

175

Add two zeros.

17,500

Multiply 25 by 2

50

Add a zero.

500.

17500 + 500 = 18000