Now, a new operation is defined, for numbers a and B, a} B = a + B / 1-ab. try to calculate (1 / 2} 1 / 5)} 1 / 8

Now, a new operation is defined, for numbers a and B, a} B = a + B / 1-ab. try to calculate (1 / 2} 1 / 5)} 1 / 8

（1/2*1/5)*（1/8)
=[(1/2+1/5)/(1-1/2 ×1/5)]*(1/8)
=(7/9)*(1/8)
=(7/9+1/8)/(1-7/9 ×1/8)
=65/65
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Add several plus signs to the following 1, 2, 3, 4, 5, 6, 7, 8 and 9 to get 99 {adjacent numbers can be used

12+3+4+56+7+8+9=99
1+23+45+6+7+8+9=99
1+2+3+4+5+67+8+9=99
Idea: 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45, 54 different from 99. If you remove a plus sign, it is equivalent to making the previous number ten times the original number, that is, increasing by 9 times. 54 △ 9 = 6, so as long as you make the number of ten digits add up to 6