How to solve a simple problem 4.05-2.8-0.7 Write clearly and get the right number to score

How to solve a simple problem 4.05-2.8-0.7 Write clearly and get the right number to score

4.05-2.8-0.7
=4.05-(2.8+0.7)
=0.55
Let's go to the fifth grade. Our teacher just said that

1999+19991999+199919991999 2
------------------------------------------ ---- -------------
1997+19971997+199719971997 1997
It's a fraction problem

=1999×(1+10001+100010001)/[1997×(1+10001+100010001)]-2/1997
=1999/1997-2/1997
=1997/1997
=1

252525/525525*252252/525252
2 1 / 3 + 4 1 / 5 + 6 1 / 35 + 8 1 / 63

252525/525525*252252/525252
=25×10101/525×1001 ×252×1001/52×10101
=25×252/525×52
=3/13
2 1 / 3 + 4 1 / 15 + 6 1 / 35 + 8 1 / 63
=2+4+6+8+1/3+1/15+1/35+1/63
=20+1/2(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9)
=20 and 4 / 9

Let's do two simple calculation problems
Simple calculation
（20.1-21×6/7）÷6
9/13-7/10+4/13-0.3

1. 0.3333.
2 . 0