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Question

A plank of wood 4·25 m long and 3·4 m wide is to be cut into square pieces of equal size. How many square pieces of largest size can be cut from the plank, if no wastage is allowed ?

This question was previously asked in
CDS 2 2024 Maths Question Paper (01-Sep-2024)
The correct answer is
45

Understanding the Problem

The question asks us to find the maximum number of identical square pieces that can be cut from a rectangular wooden plank measuring 4.25 m in length and 3.4 m in width. The key requirements are that the square pieces should be of the largest possible size and that there should be no wastage of wood during the cutting process.

Converting Dimensions to a Common Unit

To perform calculations accurately, especially when finding the Greatest Common Divisor (GCD), it's helpful to convert the dimensions of the plank from meters to a smaller unit, such as centimeters.

  • Length = 4.25 m = 4.25 \(\times\) 100 cm = 425 cm
  • Width = 3.4 m = 3.4 \(\times\) 100 cm = 340 cm

Determining the Largest Square Size using GCD

For the square pieces to be the largest possible size and for there to be no wastage, the side length of each square must be the Greatest Common Divisor (GCD) of the plank's length and width. The GCD is the largest positive integer that divides both numbers without leaving a remainder.

We find the GCD of 425 and 340 using prime factorization:

  • Prime factorization of 425: \(425 = 5 \times 85 = 5 \times 5 \times 17 = 5^2 \times 17\)
  • Prime factorization of 340: \(340 = 10 \times 34 = (2 \times 5) \times (2 \times 17) = 2^2 \times 5 \times 17\)

To find the GCD, we identify the common prime factors and take the lowest power of each:

Common factors are 5 and 17. \(GCD(425, 340) = 5^1 \times 17^1 = 85\).

Thus, the side length of the largest square piece that can be cut is 85 cm.

Calculating the Total Number of Square Pieces

With the side length of the largest possible square determined (85 cm), we can now calculate how many squares fit along the length and the width of the plank.

  • Number of square pieces along the length = \(\frac{\text{Plank Length}}{\text{Square Side Length}} = \frac{425 \text{ cm}}{85 \text{ cm}} = 5\)
  • Number of square pieces along the width = \(\frac{\text{Plank Width}}{\text{Square Side Length}} = \frac{340 \text{ cm}}{85 \text{ cm}} = 4\)

The total number of square pieces is found by multiplying the number of pieces that fit along the length by the number of pieces that fit along the width.

Total Number of Square Pieces = (Number along length) \(\times\) (Number along width)

Total Number of Square Pieces = \(5 \times 4 = 20\).

Based on the standard mathematical approach for finding the largest square pieces with no wastage, the calculation yields 20 pieces. This result differs from the provided answer option of 45. The method detailed above correctly applies the concepts of GCD and dimensions to solve this type of problem.

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