Geometry and TrigonometryEasy–MediumArea of a rectangle from its perimeter
Geometry and Trigonometry practice question
A rectangle has a perimeter of 30 centimetres and a length of 9 centimetres. What is its area, in square centimetres?
Answer: 54
Perimeter 2(l + w) = 30 gives l + w = 15, so the width is 15 − 9 = 6. Area = 9 × 6 = 54.
Common wrong answers
- If you answered 6
- 6 is the width. Multiply by the length for the area.
- If you answered 135
- 135 is 9 × 15, using the half-perimeter as the width instead of subtracting the length from it.
- If you answered 189
- 189 is 9 × 21, using 30 − 9 = 21 as the width. Half the perimeter is 15, and the width is 15 − 9 = 6.
More Geometry and Trigonometry questions
- Easy–Medium
A circle has a radius of 6. What is its area? (Use A = πr².) - Easy–Medium
A right triangle has legs of length 6 and 8. What is the length of the hypotenuse? - Easy–Medium
A circle has a radius of 5. What is its circumference? (Use C = 2πr.) - Easy–Medium
What is the midpoint of the segment joining the points (2, 3) and (8, 11)? - Easy–Medium
What is the measure, in degrees, of angle B? - Easy–Medium
What is the area, in square centimeters, of the trapezoid?
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