1 * 3 = 1 × 2 × 3, 4 * 5 = 4 × 5 × 6 × 7 × 8, please calculate 3 * 4

1 * 3 = 1 × 2 × 3, 4 * 5 = 4 × 5 × 6 × 7 × 8, please calculate 3 * 4

The first number starts, and the last number represents the total number
So 3 * 4 = 3 * 4 * 5 * 6, I'll type it according to your * I hope it can help you

Who knows the simple operation of 4.05 minus 2.8 minus 0.7?
It must be easy to calculate,

4.05-2.8-0.7
=4.05-(3+1)
=0.05
0.05+(0.3+0.2)=0.55
Our teacher taught us to do this. I don't know if it's OK~
The unregistered number above is also accidental. Sorry

How to divide 8.. 1 by 4.2 minus 0.3 by 2.1 plus 3 / 7

It's 8.1 / 4.2-0.3 / 2.1 + 3 / 7
The denominator * 10 is 81 / 42-3 / 21 + 3 / 7
The same denominator is 81 / 42-6 / 42 + 18 / 42
81-6 + 18 / 42 with the same denominator
The result is 93 / 42