Question four, question six and thinking surfing.

Question 4: The current selling price is: 4500 times 85%=3825.

Compared with the original price, the cheaper price is: 4500-3825=675.

So it's 675 cheaper than the original price.

Question 6: (1) The number of questions that Huanhuan always answers is 22+3=25.

So the correct rate of Huanhuan is: 22 divided by 25=0.88.

So Huanhuan's correct answer rate is 88%

(2) The number of questions that Huanhuan always answers correctly is 0.92 times 25=23.

So the number of questions Huanhuan answered incorrectly is 25-23=2.

Thinking Surfing: The total number of parts processed by * * * is 160+40=200.

Number of unqualified pieces: 8 pieces

Number of qualified parts in all processed parts: 200-8= 192.

Qualified rate of machined parts: 192 divided by 200=0.96.

So the pass rate is 96%