The height of 1.A is 90% of that of B, and A is shorter than B (10)%.

( 1-90%)/ 1= 10%

2. Three of the 60 products were unqualified, and the qualified rate was 95%.

(60-3)/60* 100%=95%

3. Dissolve 20g of salt in180g of water, and the salt content of brine is (10)%.

20/(20+ 180)* 100%= 10%

4. 25% less than 1000m is (750 m); 20% over 20 tons is (24) grams.

1000- 1000 * 25% = 750(m)； 20+20*20%=24 (g)

5,40 is 20% less than (50); 60 is 20% more than (50)

40/( 1-20%)=50; 60/( 1+20%)=50

6. There are 20 boys and 25 girls, with 20% fewer boys and 25% more girls than boys.

(25-20)/25=20%; (25-20)/20=25%