0.1+0.2 == 0.30000000000000004
 
0.1 + 0.7 == 0.7999999999999999
 
7*0.8 == 5.6000000000000005
 
5.6/7 == 0.7999999999999999

0.1+0.2 =》　(1+2)/10 == 0.3
 
0.1 + 0.7 =》 (1+7)/10 == 0.8
 
7*0.8 == (7*8)/10 == 5.6
 
5.6/7 == (56/7)/10 == 0.1

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  0.1+0.2
=> JSMath(0.1).add(0.2).value == 0.3
 
7+0.8
=> JSMath(7).times(0.8).value == 5.6
 
5.6/7
=> JSMath(5.6).div(7).value = 0.8

  0.05 + 0.05 + 0.2
=> JSMath(JSMath(0.05).add(0.05)).add(0.2).value == 0.3
 
(5+0.6)/7
=> JSMath(JSMath(5).add(0.6)).div(7).value == 0.8