8.7 * 9.9 simple calculation

8.7 * 9.9 simple calculation

8.7*9.9
=8.7x(10-0.1)
=8.7x10-8.7x0.1
=87-0.87
=86.13
What I don't understand is questioning

Simple calculation of 7.09 * 10.8-0.8 * 7.9
Such as the title
In a quarter of an hour
It seems to be a mistake

7.09*10.8-0.8*7.9
=76.572-6.32
=70.252
This question can't be simplified. You copied it wrong
7.09*10.8-0.8*7.09
=7.09*（10.8-0.8）
=70.9
If you don't believe in yourself, take a good look at the problem

How to calculate (313 + 5 / 6 + 7 / 8 + 9 / 10) / (5 / 6 + 7 / 8 + 9 / 10)?

（313+5/6+7/8+9/10）/（5/6+7/8+9/10）
=313+(5/6+7/8+9/10)/(5/6+7/8+9/10)
=313+1
=314