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SSC CGL level Solution Set 18, Geometry 1

Eighteenth Solution Set on SSC CGL level problems and 1st on Geometry

SSC CGL solution set 18 geometry1

This is the 18th solution set of 10 practice problem exercise for SSC CGL exam and 1st on Geometry. The questions generally are on basic concepts on triangles and a few on circles also. Students are expected to solve the corresponding question set before referring to this solution set.

We will repeat here the method of taking the test if you have not gone through it already. And if you have not taken the test yet, you can refer to SSC CGL Question Set 18, Geometry 1, and then after taking the test come back to this solution.

Method for taking the test and get the best results from the test set:

  1. Before start, go through the tutorials Geometry basic concepts part 1, points lines and triangles, Geometry basic concepts part 2, Quadrilaterals squares, Geometry basic concepts part 3, Circle, Basic and Rich concepts Geometry Part 4 on proof of arc angle subtending concepts, Basic and Rich concepts Geometry Part 5 on proof of median relations or any other short but good material to refresh your concepts if you so require. This question set is in fact the set of exercise problems at the end of the first tutorial. Don't do the exercise as you are preparing for a hard competitive test. For you, taking the test will involve a different more stringent method.
  2. Answer the questions in an undisturbed environment with no interruption, full concentration and alarm set at 12 minutes.
  3. When the time limit of 12 minutes is over, mark up to which you have answered, but go on to complete the set.
  4. At the end, refer to the answers given at the end to mark your score at 12 minutes. For every correct answer add 1 and for every incorrect answer deduct 0.25 (or whatever is the scoring pattern in the coming test). Write your score on top of the answer sheet with date and time.
  5. Identify and analyze the problems that you couldn't do to learn how to solve those problems.
  6. Identify and analyze the problems that you solved incorrectly. Identify the reasons behind the errors. If it is because of your shortcoming in topic knowledge improve it by referring to only that part of concept from the best source you get hold of. You might google it. If it is because of your method of answering, analyze and improve those aspects specifically.
  7. Identify and analyze the problems that posed difficulties for you and delayed you. Analyze and learn how to solve the problems using basic concepts and relevant problem solving strategies and techniques.
  8. Give a gap before you take a 10 problem practice test again.

Important: both practice tests and mock tests must be timed, analyzed, improving actions taken and then repeated. With intelligent method, it is possible to reach highest excellence level in performance.

Eighteenth Solution set- 10 problems for SSC CGL exam: 1st on Geometry - time to answer 12 mins

Problem 1.

$\triangle ABC$ is an isosceles triangle with $AB=AC$ and $AD$ as the median to base $BC$. If $\angle ABC = 35^0$, the $\angle BAD$ is

  1. $70^0$
  2. $35^0$
  3. $55^0$
  4. $110^0$

Solution 1.

The following isosceles triangle has its $\angle ABC = 35^0$ and AB = AC.

SSC CGL Solution Set 18 geometry1 q1

As $AD$ is median to the base $BC$, it bisects the side $BC$ so that, $BD=DC$. In two triangles, $\triangle ABD$ and  $\triangle ACD$ with common side $AD$ all three pairs of corresponding sides are equal to each other and so the triangles are congruent. This gives us, $\angle ADB = \angle ADC = 90^0$. And so the $\angle BAD = 180^0  - 35^0 - 90^0 = 55^0$.

Answer: Option c: $55^0$.

Problem 2.

In isosceles triangle $\triangle FGH$,  $FG \lt 3$cm and $GH = 8$cm. Then the correct relation is,

  1. $GH = FH$
  2. $GH \lt FH$
  3. $GF = GH$
  4. $FH \gt GH$

Solution 2.

If $FG \lt 3$cm, it is less than half of the second side $GH=8$cm. It means if in the isosceles triangle, the third side equals the smaller side, the two of them will be smaller than the other side $GH$ which violates the basic condition of formation of a triangle. The basic law of formation of a triangle states,

Sum of lengths of any two sides of a triangle must be larger than the third side.

Thus, the equal sides are the larger sides, that is, $GH = FH = 8$cm.

Answer: Option a: $GH = FH$.

Problem 3.

The sum of three altitudes of a triangle is,

  1. equal to the sum of three sides
  2. twice the sum of sides
  3. greater than the sum of sides
  4. less than the sum of sides

Solution 3.

SSC CGL Solution Set 18 geometry1 q3

The altitudes of the triangle $\triangle ABC$ are $AD$, $BE$ and $CF$. As these are the heights, these are the shortest distances to the opposite sides, that is, a height is lesser in length than both its adjacent sides. To be specific, the length of $AD$ will be less than both the adjacent sides, $AB$ and $AC$. This will be true for the other two altitudes $BE$ and $CF$. So if you add up One adjacent side corresponding to each height, the sum of heights will always be less than the sum of three sides.

For example we may add up, $BA$ for $AD$, $AC$ for $CF$ and $CB$ for $BE$.

Or, $(AD + CF + BE) \lt (BA + AC + CB)$,

as, $AD \lt BA$, $CF \lt AC$ and $BE \lt CB$.

Answer: Option d: less than the sum of sides.

Problem 4.

The length of 3 sides of a triangle are, 6cm, 8cm and 10cm. The length of the median to the greatest side is then,

  1. 5cm
  2. 8cm
  3. 4.8cm
  4. 6cm

Solution 4.

SSC CGL Solution Set 18 geometry 1 q4

As $6^2 + 8^2 = 10^2$ in the given triangle, it is a right triangle $\triangle ABC$ with base side $AB = 8$cm, height side $AC = 6$cm  and hypotenuse $BC = 10$cm. $AD$ is the median drawn from $A$ to center point $D$ of largest side $BC$.

We know that the diameter of a circle subtends an angle of $90^0$ at its periphery and so we may consider the three vertices of the triangle to lie on the periphery of the circumscribing circle with diameter as $BC$ and center at $D$. So, $AD$ will be another radius and will be equal to $BD=5$cm.

Answer: a: 5cm.

Problem 5.

$O$ and $C$ are the Orthocenter and the Circumcenter of an acute angled triangle $\triangle PQR$ respectively. The points $P$ and $O$ are joined and produced to meet the side $QR$ at $S$. If $\angle QCR = 130^0$ and $\angle PQS = 60^0$ then $\angle RPS$ is,

  1. $100^0$
  2. $35^0$
  3. $30^0$
  4. $60^0$

Solution 5.

The following is the circumscribed triangle that depicts the problem.

SSC CGL Solution set 18 Geometry 1 q5

The chord $QR$ subtends an angle $\angle QCR=130^0$ at the center that is double the $\angle RPQ$ subtended at the periphery. So, $\angle RPQ=65^0$.

Again in right-angled $\triangle PQS$, $\angle PQS = 60^0$. So, the other angle in the $\triangle PQS$, $\angle QPS = 30^0$.

Finally then, desired $\angle RPS = \angle RPQ - \angle QPS = 65^0 - 30^0 = 35^0$.

Answer: b: $35^0$.

Problem 6.

If $I$ is the incenter of $\triangle ABC$,  $\angle ABC = 65^0$ and $\angle ACB = 55^0$, the $\angle BIC$ is,

  1. $110^0$
  2. $120^0$
  3. $130^0$
  4. $140^0$

S0lution 6.

The following is the picture that depicts the problem.

SSC CGL Solution Set 18 geometry1 q6

In $\triangle BIC$ as $BI$ and $CI$ are angle bisectors,

$\angle BIC = 180^0 - \frac{1}{2}(\angle ABC + \angle ACB)$

$\hspace{13mm}= 180^0 - \frac{1}{2}(65^0 + 55^0)$


Answer: b: $120^0$.

Problem 7.

If the median drawn on the base of a triangle is half its base, the triangle will be,

  1. acute-angled
  2. obtuse-angled
  3. right-angled
  4. equilateral

Solution 7.

SSC CGL Solution Set 18 geometry1 q7

The median $AD$ drawn on the base $BC$ of the triangle $\triangle ABC$, is equal to half of $BC$, that is, $AD=BD=DC$. This is the situation where we can consider the point $D$ as the center of a circle with the three points $A$, $B$ and $C$ lying on the periphery of the circle and $AD=BD=CD$ as the radii and $BC$ as the diameter. As the diameter subtends an angle of $90^0$, the triangle is a right angled triangle.

Answer: c: right-angled.

Problem 8.

In a right angled triangle the product of its two sides equals half of the square of the third side which is the hypotenuse. One of the acute angles must then be,

  1. $15^0$
  2. $30^0$
  3. $45^0$
  4. $60^0$

Solution 8.

The following picture depicts the problem.

SSC CGL Solution Set 18 geometry1 q8

By the definition of the problem we have,

$AC\times{AB} = \frac{1}{2}BC^2$,

Or, $2AC\times{AB}=BC^2$.

Again by Pythagoras theorem,

$AC^2 + AB^2 = BC^2$.

Subtracting the first equation from the second we have,

$(AC - AB)^2 = 0$,

Or, $AC = AB$.

It means the right-angled triangle is also an isosceles triangle with angles = $45^0$.

Answer: c: $45^0$

Problem 9.

In $\triangle ABC$, two points $D$ and $E$ are taken on the lines $AB$ and $BC$ respectively in such a way that $AC$ is parallel to $DE$. The $\triangle ABC$ and $\triangle DBE$ are then,

  1. always similar
  2. always congruent
  3. similar only if $D$ lies outside the line segment $AB$
  4. congruent only if $D$ lies outside the line segment $AB$

Solution 9.

The picture below depicts the problem.

SSC CGL Solution Set 18 geometry1 q9

As $AC || DE$, in two triangles $\triangle ABC$ and $\triangle DBE$, $\angle CAB = \angle EDB$, and $\angle ACB = \angle DEB$. Apex angle being common, all three angles of $\triangle ABC$ equal the corresponding angles in $\triangle DBE$. So the two triangles are similar to each other.

As $D$ and $E$ are moved down the sides $BA$ and $BC$ respectively keeping the paralellism of $AC||DE$ undisturbed, the two triangles $\triangle ABC$ and $\triangle DBE$ remain similar to each other even when point $D$ lies outside the line segment $AB$.

Only when $D$ and $E$ coincide with $A$ and $C$ respectively, the two triangles become congruent to each other. But even in this case, the similarity characteristic holds.

So similarity holds always, whereas congruency hold only on one occasion.

Answer: a: always similar.

Problem 10.

$AD$ is a median of $\triangle ABC$ and $O$ is the centroid such that $AO = 10cm$. Length of $OD$ (in cm) is,

  1. 7
  2. 5
  3. 4
  4. 2

Solution 10.

SSC CGL Solution Set 18 geometry1 q10

$O$ is the centroid of the triangle $\triangle ABC$ and is the point of intersection of its three medians. As the centroid divides a median in the ratio of 2 : 1 from the vertex, in this case we have, $AO : OD = 2 : 1$. As $AO=10$cm, $OD$ is half of it, that is, 5cm.

Answer: b: 5.

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