If the length of a rectangle is reduced by 5 cm, the area will be reduced by 50 square cm. If the width is increased by 7 cm, the area will be increased by 28 square cm

Let length a and width b (CM), then (a-5) B = AB-50, that is, B = 10
(B + 7) a = AB + 28, that is, a = 4
S=ab=40

The circumference of a rectangle is 240 meters, and its length is three times of its width

Let a rectangle be x meters wide and 3 x meters long
2(x+3x)=240
4x=120
x=30
3x=3*30=90
Area: 30 × 90 = 2700 square meters

The perimeter of a rectangle is 80 meters, and the length is three times the width. How many square meters is the area of the rectangle?

Is the equation OK?
Let the width be x and the length be 3x
（X+3X）×2=80
4X=40
X = 10m
The width is 10 meters and the length is 10 × 3 = 30 meters
Area = 10 × 30 = 300 square meters

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