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Question

Triangles $PQR$ and $ABC$ are similar triangles.
Triangle $ABC$ have the following sides.
$AB = 36\text{ cm}$
$AC = 20\text{ cm}$
$BC = 48\text{ cm}$
Triangle $PQR$ have the following sides:
$PQ = 9\text{ cm}$
$PR = 5\text{ cm}$
What is the length of side $RQ$ =?

This question was previously asked in
RRB ALP 2018 CBT 2 Fitter Question Paper (21-Jan-2019) (Shift 3)
The correct answer is
12 cm

Similar Triangles PQR and ABC: Finding Side RQ

The problem states that triangle $PQR$ is similar to triangle $ABC$ ($\triangle PQR \sim \triangle ABC$). This similarity implies that the ratios of their corresponding sides are equal.

Corresponding Sides Identification

Given the similarity $\triangle PQR \sim \triangle ABC$, the corresponding sides are:

  • $PQ$ corresponds to $AB$
  • $PR$ corresponds to $AC$
  • $RQ$ corresponds to $BC$

Setting Up Proportions

The property of similar triangles allows us to write the following proportion:

$ \frac{PQ}{AB} = \frac{PR}{AC} = \frac{RQ}{BC} $

Calculating the Scale Factor

We are given the lengths:

  • $AB = 36$ cm, $AC = 20$ cm, $BC = 48$ cm
  • $PQ = 9$ cm, $PR = 5$ cm

We can find the scale factor using the pairs $(PQ, AB)$ or $(PR, AC)$.

Using $PQ$ and $AB$: $ \text{Scale Factor} = \frac{PQ}{AB} = \frac{9 \text{ cm}}{36 \text{ cm}} = \frac{1}{4} $

Using $PR$ and $AC$: $ \text{Scale Factor} = \frac{PR}{AC} = \frac{5 \text{ cm}}{20 \text{ cm}} = \frac{1}{4} $

The scale factor from $\triangle ABC$ to $\triangle PQR$ is consistent and equals $\frac{1}{4}$.

Determining the Length of RQ

Now, we use the scale factor to find the length of $RQ$. We set up the proportion involving $RQ$ and its corresponding side $BC$:

$ \frac{RQ}{BC} = \text{Scale Factor} $ $ \frac{RQ}{48 \text{ cm}} = \frac{1}{4} $

To find $RQ$, multiply both sides by $48$ cm:

$ RQ = \frac{1}{4} \times 48 \text{ cm} $ $ RQ = 12 \text{ cm} $

Therefore, the length of side $RQ$ is 12 cm.

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Similar Questions

  1. It is given that, \(\Delta ABC \sim \Delta EDF\) such that \(AB = 5 \text{ cm}\), \(AC = 7.5 \text{ cm}\), \(DF = 15 \text{ cm}\) and \(ED = 12.5 \text{ cm}\). The sum of the remaining sides of the triangles is:
  2. In two triangles, ∆ABC ∼ ∆PQR, AB=12cm and PQ=4cm, if AL and PM are altitudes of the respected triangles, then what will be AL : PM?

  3. In the given figure, if \(RS = 3\sqrt{3} \text{ cm}\) and \(RPS\) is an equilateral triangle, then find the value of \(QR\)

  4. In a right angled triangle, with angle at \(A\) being \(90^\circ\), the side \(AB\) is of length 3cm and \(BC\) is 12 cm. What is the length of side \(AC\)?
  5. For a pair of similar triangles shown in the figure, the angles made at $B$ and $R$ are same in both the triangles $BAC$ and $RAQ$. If the ratio of the areas of the two triangles is 2:1, and if the area of $BAC$ is $100\text{ cm}^2$ then what is the area of $RAQ$ in sq.cm.?

  6. In a triangle $ABC$, the length of the side $AB$ is 2m, the angle at $C$ is $60^\circ$ and the angle at $B$ is $30^\circ$, what is the length of side $AC$?
  7. In a right angled triangle, with angle at A being , the side $AB$ is of length 4cm and $BC$ is 15 cm. What is the length of side $AC$?

     

     

  8. What is the area of the triangle in sq. cm. with a base of 10 cm and sides of length 6 cm each?
  9. What is the angle at $B$ in the triangle $ABC$, if the angle made at $K$ is $30^\circ$ and the triangles shown in the figure are similar?

  10. In a triangle the length of the sides, $AB$ is 3m and $BC$ is 5m what is the length of $AC$, if the angle formed at $B$ is $60^\circ$

Important Questions from Triangles

  1. Among the following options, which are NOT sides of a triangle?

  2. In a Δ ABC, if ∠A = 120° and AB = AC, then the values of ∠B and ∠C are respectively:

  3. In the equilateral Δ ABC, the base BC is trisected at D and E. The line through D, Parallel to AB, meets AC at F and the line through E parallel to AC meets AB at G. If EG and DF intersect at H, then what is the ratio of the sum of the area of parallelogram AGHF and the area of the Δ DHE to the area of the Δ ABC?

  4. The product of the perimeter of a triangle, the radius of its in‐circle, and a number gives the area of the triangle. The number is

  5. A man goes 24 m towards east and then 10 m towards north. How far is he away from his initial position?

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