Oblongs  - A Maths Starter Of The Day

Find the length and width of a rectangle if its perimeter is 24cm and area is 35cm2.

What are the dimensions of a rectangle whose perimeter is 62cm and area is 168cm2.

Find the dimensions of a rectangle whose perimeter is 43cm and area is 114cm2.

Find the dimensions of all the rectangles whose perimeters in cm are twice the value of their areas in cm2.

A Mathematics Lesson Starter Of The Day


Topics: Starter | Area | Geometry | Mensuration | Shape | Simultaneous Equations

  • Transum,
  •  
  • The first three problems are in increasing order of difficulty. The first can probably be guessed, the second needs more of a strategy as the numbers are larger and the third involves a fraction so probably requires the application of a more generalised method. Refreshing the page generates three different rectangles to further consolidate any techniques learned in the first round. The fourth problem is only for Nobel prize candidates!
  • Simon Fletcher, Bolton UK
  •  
  • 52 cm rectangle perimeter 105 area. Is this correct? I've checked and can't find a solution.
  • Transum,
  •  
  • Hello Simon, so you are looking for two numbers (the height and the width) that add up to half the perimeter, 26cm, and multiply together to give an area of 105cm2.
    We can write two simultaneous equations showing this information:
    h + w = 26
    hw = 105
    We can combine the information in these two equations and eliminate one of the unknowns:
    From the first equation we see that h = 26 – w
    Substituting this into the second equation gives (26 – w)w = 105
    Expanding the brackets gives 26w - w2=105
    Rearranging gives w2 - 26w + 105 = 0
    This is a quadratic equation which can be solved by factorising
    (w – 5)(w – 21) = 0
    So w could be 5cm in which case h would be 21cm or, w could be 21cm in which case h would be 5cm.
  • Audrey Macmillan, @audproctor77
  •  
  • Clarifying area/perimeter confusion using a Transum Starter. Great #mathschat on squares and rows.

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Answers




3 and 3/2

4 and 4/3

5 and 5/4

6 and 6/5

7 and 7/6

8 and 8/7

9 and 9/8

10 and 10/9

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Laptops In Lessons

Teacher, do your students have access to computers such as tablets, iPads or Laptops?  This page was really designed for projection on a whiteboard but if you really want the students to have access to it here is a concise URL for a version of this page without the comments:

Transum.org/go/?Start=April3

However it would be better to assign one of the student interactive activities below.

Laptops In Lessons

Here are URLs which will take them to related student activities.

Transum.org/go/?to=Oblongs

Student Activity

Transum.org/go/?to=AreaBuilder

Student Activity

 


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