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Question

A rectangle becomes a square when its length and breadth are reduced by 10 m and 5 m, respectively. During this process, the rectangle loses 650 m2 of area. What is the area of the original rectangle in square meters?

The correct answer is

2250

To find the area of the original rectangle, we need to determine its initial length and breadth. We are given information about how the rectangle transforms into a square and the area lost during this process.

Rectangle Dimensions and Transformation

Let the original length of the rectangle be \(L\) meters and the original breadth be \(B\) meters.

The area of the original rectangle is \(A_{\text{original}} = L \times B\) square meters.

  • The length is reduced by 10 m, so the new length is \((L - 10)\) m.
  • The breadth is reduced by 5 m, so the new breadth is \((B - 5)\) m.

After these reductions, the rectangle becomes a square. This means that the new length and the new breadth must be equal:

\[L - 10 = B - 5\]

We can rearrange this equation to express \(L\) in terms of \(B\):

\[L = B - 5 + 10\]

\[L = B + 5 \quad \text{(Equation 1)}\]

Area Loss Calculation

The area of the new square is \(A_{\text{new}} = (L - 10)(B - 5)\) square meters.

We are told that the rectangle loses 650 m\(^2\) of area during this process. This means the difference between the original area and the new area is 650 m\(^2\):

\[A_{\text{original}} - A_{\text{new}} = 650\]

Substitute the expressions for the areas:

\[L \times B - (L - 10)(B - 5) = 650\]

Now, expand the term \((L - 10)(B - 5)\):

\[(L - 10)(B - 5) = LB - 5L - 10B + 50\]

Substitute this back into the area loss equation:

\[LB - (LB - 5L - 10B + 50) = 650\]

Distribute the negative sign:

\[LB - LB + 5L + 10B - 50 = 650\]

The \(LB\) terms cancel out:

\[5L + 10B - 50 = 650\]

Add 50 to both sides:

\[5L + 10B = 650 + 50\]

\[5L + 10B = 700\]

Divide the entire equation by 5 to simplify:

\[L + 2B = 140 \quad \text{(Equation 2)}\]

Solving for Original Dimensions

Now we have a system of two linear equations with two variables:

  1. \(L = B + 5\)
  2. \(L + 2B = 140\)

Substitute the expression for \(L\) from Equation 1 into Equation 2:

\[(B + 5) + 2B = 140\]

Combine like terms:

\[3B + 5 = 140\]

Subtract 5 from both sides:

\[3B = 140 - 5\]

\[3B = 135\]

Divide by 3 to find the value of \(B\):

\[B = \frac{135}{3}\]

\[B = 45 \text{ meters}\]

Now that we have the breadth, substitute \(B = 45\) back into Equation 1 to find the length:

\[L = B + 5\]

\[L = 45 + 5\]

\[L = 50 \text{ meters}\]

Original Rectangle Area

Finally, we can calculate the area of the original rectangle using its length and breadth:

\[\text{Original Area} = L \times B\]

\[\text{Original Area} = 50 \text{ m} \times 45 \text{ m}\]

\[\text{Original Area} = 2250 \text{ m}^2\]

The area of the original rectangle is 2250 square meters.

Parameter Value
Original Length (\(L\)) 50 m
Original Breadth (\(B\)) 45 m
Original Area (\(L \times B\)) \(50 \times 45 = 2250\) m\(^2\)
New Length (\(L-10\)) \(50-10 = 40\) m
New Breadth (\(B-5\)) \(45-5 = 40\) m
New Area (\((L-10)(B-5)\)) \(40 \times 40 = 1600\) m\(^2\)
Area Lost \(2250 - 1600 = 650\) m\(^2\)

This confirms our calculations align with the problem statement.

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Important Questions from Numerical Computation

  1. A cube of side 3 units is formed using a set of smaller cubes of side 1 unit. Find the proportion of the number of faces of the smaller cubes visible to those which are NOT visible.

  2. What is the average of all multiples of 10 from 2 to 198?

  3. Ratio of the angles of a triangle are 1 : 2 : 6. What is the smallest angle?

  4. A deposit in a bank, which pays interest on its deposits compounded daily, grows to Rs. 80,000 for 500 days and to 88,000 for 1000 days. What would be its value (in Rs.) for 1500 days?

  5. Among A, B, C and D, there is a lawyer, a doctor, a teacher and a journalist. They drink exactly one each of tea, coffee, lemonade and milk. If neither the lawyer nor the teacher drinks milk, B drinks coffee, A is the teacher and C is the doctor and drinks tea, then which of the following is FALSE?

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