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Logical Deduction - Aptitude Questions and Answers - RejinpaulPlacement

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In each of the questions below are given statements followed by four conclusions numbered I, II, III and IV, You have to take the given statements to be true even if they seem to be at variance from the commonly known facts. Read all the conclusions and then decide which of the given conclusions logically follows from the given statements disregarding commonly known facts.

16.
Statements:Some spoons are bowls. All bowls are knives. All knives are forks.

Conclusions:
I.All spoons are forks.
II.All bowls are forks.
III.Some knives are bowls.
IV.Some forks are spoons.
Answer & Solution
Answer: (D) None of these

Solution: III is the converse of the second premise and so it holds. Some spoons are bowls. All bowls are knives. Since one premise is particular, the conclusion must be particular and should not contain the middle term. So, it follows that 'Some spoons are knives'. All bowls are knives. All knives are forks. Since both the premises are universal and affirmative, the conclusion must be universal affirmative and should not contain the middle term. So, it follows that. 'All bowls are forks'. Thus, II follows. Some spoons are knives. All knives are forks. Since one premise is particular, the conclusion must be particular and should not contain the middle term. So, it follows that 'Some spoons are forks'. IV is the converse of this conclusion and so it follows. Hence, II, III and IV follow.
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17.
Statements: Some tigers are lions. Some lions are rabbits. Some rabbits are horses.

Conclusions:
I.Some tigers are horses.
II.Some rabbits are tigers.
III.Some horses are lions.
IV.All horses are rabbits.
Answer & Solution
Answer: (B) None follows

Solution: Since each combination of premises shall contain two particular premises, no definite conclusion can be drawn.
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18.
Statements:All oceans are rivers. Some springs are rivers. All wells are springs.

Conclusions:
I.Some springs are oceans.
II.Some wells are rivers.
III.Some rivers are oceans.
IV.No well is river.
Answer & Solution
Answer: (C) Only either II or IV, and III follow

Solution: III is the converse of the first premise and so it holds. All oceans are rivers. Some springs are rivers. Since the middle term 'rivers' is not distributed even once in the premises, no definite conclusion follows. All wells are springs. Some springs are rivers. Since the middle term 'springs' is not distributed even once in the premises, no definite conclusion follows. However, II and IV involve the extreme terms and form a complementary pair. Thus, either II or IV follows.
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19.
Statements: All doors are buses. All buses are leaves. No leaf is a flower.

Conclusions:
I.No flower is a door.
II.No flower is a bus.
III.Some leaves are doors.
IV.Some leaves are buses.
Answer & Solution
Answer: (A) All follow

Solution: IV is the converse of the second premise and so it holds. All doors are buses. All buses are leaves. Since both the premises are universal and affirmative, the conclusion must be universal affirmative and should not contain the middle term. So, it follows that 'All doors are leaves'. III is the converse of this conclusion and so it holds. All buses are leaves. No leaf is a flower. Since both the premises are universal and one premise is negative, the conclusion must be universal negative and should not contain the middle term. So, it follows that 'No bus is flower'. II is the converse of this conclusion and so it holds. All doors are buses. No bus is flower. As discussed above, it follows that 'No door is flower'. I is the converse of this conclusion and so it also holds.
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20.
Statements:Some trains are roads. No road is jungle. All flowers are jungles.

Conclusions:
I.Some trains are flowers.
II.Some trains are jungles.
III.Some flowers are trains.
IV.No road is flower.
Answer & Solution
Answer: (D) Only IV follows

Solution: Some trains are roads. No road is jungle. Since one premise is particular and the other negative, the conclusion must be particular negative and should not contain the middle term. So, it follows that 'Some trains are not jungles'. No road is jungle. All flowers are jungles. Since both the premises are universal and one premise is negative, the conclusion must be universal negative and should not contain the middle term. So, it follows that 'No flower is road'. IV is the converse of this conclusion and so it holds. Some trains are roads, No flower is road. As discussed above, it follows that 'Some trains are not flowers'.
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