1. If the annual interest rate of one-year fixed deposit in the bank is 2.25%, when Xiaoli's father takes out the principal and interest due in one year, 27 yuan will deduct the interest tax and ask Xiaoli's father how much principal he has saved.

The principal deposited by Xiao Li's father is X yuan.

X*2.25%*20%=27

X*0.0225*0.2=27

0.0225X= 135

X=6000

2. A store marked the cost price of a dress as 40% and sold it at a 20% discount. As a result, each piece of clothing still earned 15 yuan. What is the cost price of each piece of clothing?

Suppose the cost price of each piece of this kind of clothing is X yuan.

X*( 1+40%)*80%- 15=X

X* 1.4*0.8-X= 15

0. 12X= 15

X= 125

In the model airplane competition, the first model airplane flew 480 meters less than the second model airplane. It is known that the speed of the first model is faster than that of the second model 1m/s, and the flight time of the two models is 12 minutes and 16 minutes respectively. How far did these two model planes fly?

Suppose the first plane flew x meters, then the second plane flew X+480 meters.

12min = 720s,16min = 960s.

X/720=(X+480)/960+ 1

4X=3(X+480)+2880

4X=3X+ 1440+2880

X=4320

4320+480=4800

A:

The first plane and the second plane flew 4320 meters and 4800 meters respectively.