Solution: Let the side length of the original square be x cm.

Analysis:

The length and width of the strips cut for the first time are x and 4cm respectively.

The second cut strip is x-4cm long and 5cm wide.

Equivalence relation: the areas of the two belts are equal.

4x=5(x-4)

4x=5x-20

x=20

Area of each strip: 4×20=80 cm2.

2.

Solution: Let the scheduled time be x hours.

Analysis:

The speed is 30, and the actual time is x- 12/60 hours.

The speed is 24, and the actual time is x+6/60 hours.

Equivalence relation: AB distance is equal

30(x- 12/60)=24(x+6/60)

30x-6=24x+2.4

6x=8.4

x= 1.4

AB distance: 30 (1.4-12/60) = 30 *1.2 = 36 km.

Another solution:

Let AB distance be x kilometers.

Analysis:

Speed 30, time x/30, scheduled time x/30+ 12/60.

Speed 24, time x/24, scheduled time x/24- 10/60.

Equivalence relation: the predetermined time is equal

x/30+ 12/60=x/24-6/60

Multiply it by 120 at the same time to get:

4x+24=5x- 12

x= 12+24

x=36

3.

Solution: Set the outage time as x hours.

Analysis:

Thick candles burn every hour 1/3, x/3.

Thin candles burn every hour 1/2, x/2.

Equivalence relation: the remaining length of thick candle = 2 times the remaining length of thin candle.

1 x/3 = 2( 1 x/2)

1-x/3=2-x

x-x/3=2- 1

2/3*x= 1

x=3/2( 1.5)

A: The power outage time is 3/2( 1.5) hours.