1, answer b

Analysis: If the task quantity is regarded as the unit of 1, then

Party A, Party B and Party C cooperate to complete the total task every hour 1/3, and Party A and Party B cooperate to complete the total task every hour 1/5.

Therefore,1/3-1/5 = 2/15 of the total task is completed every hour.

∴c The time required to do this alone is 1÷(2/ 15)=7.5 hours.

2. answer d

3. answer d

Analysis: Based on the original price of goods 1, the price after the first price reduction is 1×( 1-20%)=0.8.

After the second price reduction, the price is 0.8×( 1- 10%)=0.72.

Lower than before the price reduction:

( 1-0.72)÷ 1=28%

The answer is wrong by 38%. The high school teacher told you: Don't blindly believe the answer.