1. That is to say, the proportion of salt has increased. Or add salt. Or evaporate some water.

2/7, a simpler idea, can assume that B = 5, then A = 7, B is 2/7 less than A, and A is more than B, that is, (a-b)/b=(40)%.

3. 1234565432 1/777777×999999= 1234565432 1/7/ 1 1 1 1 1 1×9× 1 1 1 1 1 1= 1234565432 1/7×9

Then I'm not sure. . .

4. 1-5/6+7/ 12-9/20+ 1 1/30- 13/42+ 15/56- 17/72

= 1-( 1/2+ 1/3)+( 1/3+ 1/4)-( 1/4+ 1/5)+( 1/5+ 1/6)-( 1/6+ 1/7)+( / kloc-0//7+ 1/8)-( 1/8+ 1/9)= 1/2- 1/9=7/ 18