A square and a rectangle have the same perimeter. The side of the square is 40 cm and the length of a rectangle is 10 cm, find a breadth of rectangle. (A) 80 cm (B) 90 cm (C) 70 cm (D) None
Answer
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Hint: Let ${P_1}$= perimeter of square and ${P_2}$= perimeter of rectangle; side of square\[S = 40\], length of rectangle$L = 10$and B be the unknown breadth of the rectangle. Given that ${P_1} = {P_2}$. Use the formulae of perimeter: ${P_1} = 4 \times S$ and ${P_2} = 2 \times (L + B)$ Find B by solving the equation.
Complete step by step answer: We are given two geometrical figures - a square and a rectangle. Both have the same perimeter. We are also given some of their dimensions: Side of the square = 40 cm Length of the rectangle = 10 cm.
We are asked to compute the missing dimension of the rectangle, namely, the breadth of the rectangle. We know that for a square, its perimeter is the sum of all its sides. A square has 4 sides of equal length. This gives us the formula for the perimeter of a square. Perimeter of a square $ = 4 \times side$ Now, a rectangle has 4 sides too. But they are of varying lengths. That is, only the opposite sides are equal. So, if L denotes the length and B denotes the breadth of a rectangle, then its perimeter is given by the formula: Perimeter of a rectangle \[ = 2 \times (L + B)\] Call the side of the given square as S and its perimeter as ${P_1}$. Similarly, call the perimeter of the rectangle as ${P_2}$ Then ${P_1} = 4 \times S$ and ${P_2} = 2 \times (L + B)$ Now we have \[S = 40\] Therefore, \[{P_1} = 4 \times S = 4 \times 40 = 160\] Also, $L = 10$ and $B = ?$ implies that ${P_2} = 2 \times (L + B) = 2 \times (10 + B)$ According to the given condition, the perimeter of the square = perimeter of a rectangle. $ \Rightarrow {P_1} = {P_2} \\ \Rightarrow 160 = 2 \times (10 + B) \\ \Rightarrow 160 \div 2 = 10 + B \\ \Rightarrow 80 = 10 + B \\ \Rightarrow 80 - 10 = B \\ \Rightarrow 70 = B \\ \Rightarrow B = 70 \\ $ Hence, the breadth of the given rectangle is 70 cm.
Note: You may come across questions where width is used instead of breadth. However, both mean the same.
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