The addition and subtraction with the same denominator finally equals 1, which is easy to calculate.
Second question: add up by bit, 2.3456 = 2+0.3+0.04+0.005+0.0006, 3.4562 = 3+0.4+0.05+0.006+0.0002.
Adding the same numbers = 2+3+4+5+6+0.2+0.3+0.4+0.5+0.6+0.02+0.03+0.04+0.05+0.06+... 0.0002+0.0003+0.0004+0.
The third question 2004× 2003-2003× 2002+2002× 2006 5438+0+…+2×1= the first two operations, 2003 (2004-2002)+2006 5438+0 (2006 5438)