If the travel agency launches a travel plan with no more than 25 people, the per capita cost is 1 1,000 yuan. If there are more than 25 people, the per capita travel expenses will be reduced by 20 yuan for each additional person, but the per capita expenses shall not be lower than the charging standard in 700 yuan. How many people will take part in the tour when the employees of a certain unit spend 27,000 yuan on the tour?

Solution: First, judge.

There are more than 25 people in this unit.

Because if there are 25 people, then the amount of money used is 25 ×1000 = 25,000 yuan.

So more than 25 people

Suppose one person is added, and the per capita cost is 1000-20a-20 yuan.

( 1000-20a)×(25+a)=27000

25000-500a+ 1000a-20a？ =27000

20a？ -500 Amps +2000=0

Answer? -25a+ 100=0

(a-5)(a-20)=0

A=5 or 20

When a=20, the per capita cost = 1000-20× 20 = 600.

So a=20 doesn't matter, so I gave up.

So 25+5=30 people travel.