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15 min SSC & and Railway math set

15 mins SSC & Railways Math Set 19 Solution

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1. Question / प्रश्न

If P(x) leaves remainder 5 when divided by (x−2) and remainder 7 when divided by (x−3), then the remainder when P(x) is divided by (x−2)(x−3) is:

यदि P(x) को (x−2) से भाग देने पर शेष 5 तथा (x−3) से भाग देने पर शेष 7 प्राप्त होता है, तो P(x) को (x−2)(x−3) से भाग देने पर शेषफल क्या होगा?

Answer / उत्तर: 2x + 1

Solution / हल:

Remainder will be linear: ax + b

P(2) = 5

2a + b = 5

P(3) = 7

3a + b = 7

Subtract:

a = 2

Now, 2a + b = 5

4 + b = 5

b = 1

Remainder = 2x + 1

2. Question / प्रश्न

If x + 1/x = 3, find x⁷ + 1/x⁷.

यदि x + 1/x = 3 है, तो x⁷ + 1/x⁷ ज्ञात कीजिए।

Answer / उत्तर: 843

Solution / हल:

Let Sn = xⁿ + 1/xⁿ

S1 = 3

S2 = S1² - 2

= 3² - 2 = 7

S3 = S1 × S2 - S1

= 3 × 7 - 3 = 18

S4 = 3 × 18 - 7 = 47

S5 = 3 × 47 - 18 = 123

S6 = 3 × 123 - 47 = 322

S7 = 3 × 322 - 123 = 843

3. Question / प्रश्न

If f(f(x)) = 4x + 3 and f(x) = ax + b, then a + b equals:

यदि f(f(x)) = 4x + 3 तथा f(x) = ax + b है, तो a + b का मान क्या है?

Answer / उत्तर: 3

Solution / हल:

f(x) = ax + b

f(f(x)) = a(ax + b) + b

= a²x + ab + b

Given:

a²x + ab + b = 4x + 3

So,

a² = 4

a = 2

ab + b = 3

b(a + 1) = 3

b(2 + 1) = 3

3b = 3

b = 1

a + b = 2 + 1 = 3

4. Question / प्रश्न

The least positive integer satisfying N ≡ 1 (mod 4), N ≡ 2 (mod 5), N ≡ 3 (mod 7) is:

N ≡ 1 (mod 4), N ≡ 2 (mod 5), N ≡ 3 (mod 7) को संतुष्ट करने वाली सबसे छोटी धनात्मक संख्या क्या है?

Answer / उत्तर: 17

Solution / हल:

Check 17:

17 ÷ 4 gives remainder 1

17 ÷ 5 gives remainder 2

17 ÷ 7 gives remainder 3

So, least positive integer = 17

5. Question / प्रश्न

The number of trailing zeros in 100! is:

100! में अंतिम शून्यों की संख्या कितनी है?

Answer / उत्तर: 24

Solution / हल:

Trailing zeros depend on number of 5s in 100!

Number of 5s = 100/5 + 100/25

= 20 + 4

= 24

6. Question / प्रश्न

How many 5-digit numbers can be formed using digits 1,2,3,4,5 without repetition such that 1 and 2 are never adjacent?

1,2,3,4,5 अंकों से बिना पुनरावृत्ति के कितनी 5-अंकीय संख्याएँ बन सकती हैं जिनमें 1 और 2 साथ न हों?

Answer / उत्तर: 72

Solution / हल:

Total arrangements = 5! = 120

When 1 and 2 are together, treat them as one block.

Blocks = (12), 3, 4, 5

Arrangements = 4! × 2!

= 24 × 2

= 48

Not adjacent = 120 - 48 = 72

7. Question / प्रश्न

In how many ways can 4 men and 4 women be seated around a circle if men and women alternate?

4 पुरुष और 4 महिलाएँ एक वृत्त में कितने तरीकों से बैठ सकते हैं यदि पुरुष और महिलाएँ क्रमशः वैकल्पिक हों?

Answer / उत्तर: 144

Solution / हल:

First arrange 4 men around the circle:

(4 - 1)! = 3! = 6

Now 4 women can sit in 4 gaps:

4! = 24

Total ways = 6 × 24 = 144

8. Question / प्रश्न

Three fair coins are tossed. Given that at least one head appears, probability of exactly two heads is:

तीन निष्पक्ष सिक्के उछाले जाते हैं। यह ज्ञात है कि कम से कम एक हेड आया है। ठीक दो हेड आने की प्रायिकता क्या है?

Answer / उत्तर: 3/7

Solution / हल:

Total outcomes for 3 coins = 8

At least one head means exclude TTT.

Valid outcomes = 7

Exactly two heads outcomes:

HHT, HTH, THH

Number = 3

Probability = 3/7

9. Question / प्रश्न

A box contains 4 red and 6 blue balls. Two balls are drawn. If the first ball is red, probability second is blue is:

एक डिब्बे में 4 लाल और 6 नीली गेंदें हैं। दो गेंदें निकाली जाती हैं। यदि पहली गेंद लाल है, तो दूसरी के नीली होने की प्रायिकता क्या है?

Answer / उत्तर: 2/3

Solution / हल:

Initially red = 4, blue = 6

First ball is red, so remaining balls = 9

Blue balls still = 6

Probability second is blue = 6/9 = 2/3

10. Question / प्रश्न

If P(A)=1/2, P(B)=1/3 and P(A∩B)=1/6, then P(A∪B) equals:

यदि P(A)=1/2, P(B)=1/3 तथा P(A∩B)=1/6 है, तो P(A∪B) क्या होगा?

Answer / उत्तर: 2/3

Solution / हल:

P(A∪B) = P(A) + P(B) - P(A∩B)

= 1/2 + 1/3 - 1/6

= 3/6 + 2/6 - 1/6

= 4/6 = 2/3

11. Question / प्रश्न

The area of triangle formed by points (1,2), (4,6) and (8,3) is:

बिंदुओं (1,2), (4,6) तथा (8,3) से बने त्रिभुज का क्षेत्रफल क्या है?

Answer / उत्तर: 12.5

Solution / हल:

Area = 1/2 |x1(y2 - y3) + x2(y3 - y1) + x3(y1 - y2)|

= 1/2 |1(6 - 3) + 4(3 - 2) + 8(2 - 6)|

= 1/2 |3 + 4 - 32|

= 1/2 × 25

= 12.5

12. Question / प्रश्न

Distance between parallel lines 4x + 3y + 5 = 0 and 4x + 3y − 20 = 0 is:

समानांतर रेखाओं 4x + 3y + 5 = 0 तथा 4x + 3y − 20 = 0 के बीच की दूरी क्या है?

Answer / उत्तर: 5

Solution / हल:

Distance between parallel lines ax + by + c1 = 0 and ax + by + c2 = 0:

Distance = |c1 - c2| / √(a² + b²)

= |5 - (-20)| / √(4² + 3²)

= 25 / √25

= 25/5

= 5

13. Question / प्रश्न

The centroid of triangle with vertices (0,0), (6,0), (0,9) is:

शीर्ष (0,0), (6,0), (0,9) वाले त्रिभुज का केन्द्रक क्या है?

Answer / उत्तर: (2,3)

Solution / हल:

Centroid = ((x1 + x2 + x3)/3, (y1 + y2 + y3)/3)

= ((0 + 6 + 0)/3, (0 + 0 + 9)/3)

= (6/3, 9/3)

= (2,3)

14. Question / प्रश्न

A sphere of radius 6 cm is melted into small spheres of radius 2 cm. Number of small spheres formed is:

6 सेमी त्रिज्या वाले गोले को पिघलाकर 2 सेमी त्रिज्या वाले छोटे गोलों में बदला जाता है। छोटे गोलों की संख्या क्या होगी?

Answer / उत्तर: 27

Solution / हल:

Number of small spheres = Volume of big sphere / Volume of small sphere

= 6³ / 2³

= 216 / 8

= 27

15. Question / प्रश्न

A cone of height 12 cm and radius 5 cm is cut parallel to base at half its height. Ratio of volume of small cone to frustum is:

12 सेमी ऊँचाई और 5 सेमी त्रिज्या वाले शंकु को आधार के समानांतर आधी ऊँचाई पर काटा जाता है। छोटे शंकु और शंकुखंड के आयतन का अनुपात क्या है?

Answer / उत्तर: 1:7

Solution / हल:

Cut is made at half height.

Small cone and original cone are similar.

Linear ratio = 1:2

Volume ratio = 1³ : 2³ = 1:8

Small cone volume = 1 part

Frustum volume = 8 - 1 = 7 parts

Ratio = 1:7

16. Question / प्रश्न

Milk and water are in ratio 7:3. If 20 litres mixture is removed and replaced by water, ratio becomes 7:5. Initial quantity was:

दूध और पानी का अनुपात 7:3 है। यदि 20 लीटर मिश्रण निकालकर पानी भर दिया जाए तो अनुपात 7:5 हो जाता है। प्रारंभिक मात्रा क्या थी?

Answer / उत्तर: 120 litres / 120 लीटर

Solution / हल:

Let initial mixture = x litres

Milk = 7x/10

Water = 3x/10

20 litres mixture removed:

Milk removed = 20 × 7/10 = 14 litres

Water removed = 20 × 3/10 = 6 litres

After replacing with water:

Milk = 7x/10 - 14

Water = 3x/10 - 6 + 20

= 3x/10 + 14

New ratio = 7:5

(7x/10 - 14)/(3x/10 + 14) = 7/5

5(7x/10 - 14) = 7(3x/10 + 14)

35x/10 - 70 = 21x/10 + 98

14x/10 = 168

x = 120 litres

17. Question / प्रश्न

A invests ₹10000 for 12 months, B invests ₹15000 for 8 months. Profit ratio is:

A ₹10000 को 12 महीने तथा B ₹15000 को 8 महीने के लिए निवेश करता है। लाभ का अनुपात क्या होगा?

Answer / उत्तर: 1:1

Solution / हल:

Profit ratio = Investment × Time

A = 10000 × 12 = 120000

B = 15000 × 8 = 120000

Ratio = 120000 : 120000

= 1:1

18. Question / प्रश्न

A train 240 m long crosses a platform in 24 sec at 54 km/h. Length of platform is:

240 मीटर लंबी ट्रेन 54 किमी/घंटा की गति से एक प्लेटफॉर्म को 24 सेकंड में पार करती है। प्लेटफॉर्म की लंबाई क्या है?

Answer / उत्तर: 120 m

Solution / हल:

Speed = 54 km/h

54 km/h = 15 m/s

Distance covered in 24 sec = 15 × 24 = 360 m

Train length + Platform length = 360

240 + Platform length = 360

Platform length = 120 m

19. Question / प्रश्न

If CP is increased by 20% and SP is increased by 32%, profit percentage changes by:

यदि क्रय मूल्य 20% बढ़ता है और विक्रय मूल्य 32% बढ़ता है, तो लाभ प्रतिशत में कितना परिवर्तन होगा?

Answer / उत्तर: Cannot be determined uniquely / निश्चित रूप से निर्धारित नहीं किया जा सकता

Solution / हल:

इस प्रश्न में original CP और original SP या original profit percentage नहीं दिया गया है।

मान लें CP = 100 और SP = 100

तो नया CP = 120

नया SP = 132

Profit% = 12/120 × 100 = 10%

लेकिन यदि original SP अलग हो, तो profit percentage अलग आएगा।

इसलिए केवल CP 20% और SP 32% बढ़ने से profit percentage का change निश्चित नहीं किया जा सकता।

20. Question / प्रश्न

If 20% discount and then 10% discount are given successively, equivalent discount is:

यदि पहले 20% तथा फिर 10% की क्रमिक छूट दी जाए, तो समतुल्य छूट क्या होगी?

Answer / उत्तर: 28%

Solution / हल:

Let marked price = 100

After 20% discount:

100 × 80/100 = 80

After 10% discount:

80 × 90/100 = 72

Final selling price = 72

Equivalent discount = 100 - 72 = 28%

21. Question / प्रश्न

In a class of 100 students, 60 study Maths, 50 Physics and 20 neither. Number studying both is:

100 विद्यार्थियों की कक्षा में 60 गणित, 50 भौतिकी पढ़ते हैं तथा 20 कोई भी नहीं पढ़ते। दोनों पढ़ने वालों की संख्या क्या है?

Answer / उत्तर: 30

Solution / हल:

Total students = 100

Neither = 20

Students studying at least one subject = 100 - 20 = 80

Maths = 60

Physics = 50

Both = Maths + Physics - At least one

= 60 + 50 - 80

= 30

22. Question / प्रश्न

If a number leaves remainder 3 when divided by 5 and remainder 4 when divided by 7, then remainder when divided by 35 is:

यदि कोई संख्या 5 से भाग देने पर 3 तथा 7 से भाग देने पर 4 शेष छोड़ती है, तो 35 से भाग देने पर शेषफल क्या होगा?

Answer / उत्तर: 18

Solution / हल:

Check numbers that leave remainder 3 when divided by 5:

3, 8, 13, 18, 23, 28, 33

Now check division by 7:

18 ÷ 7 gives remainder 4

So number leaves remainder 18 when divided by 35.

23. Question / प्रश्न

The number of positive integer solutions of x + y + z = 10 is:

समीकरण x + y + z = 10 के धनात्मक पूर्णांक हलों की संख्या कितनी है?

Answer / उत्तर: 36

Solution / हल:

For positive integer solutions of x + y + z = 10:

Number of solutions = C(10 - 1, 3 - 1)

= C(9,2)

= 9 × 8 / 2

= 36

24. Question / प्रश्न

If α and β are roots of x²−8x+12=0, then α²+β² equals:

यदि α और β, x²−8x+12=0 के मूल हैं, तो α²+β² का मान क्या है?

Answer / उत्तर: 40

Solution / हल:

For x²−8x+12=0:

α + β = 8

αβ = 12

α² + β² = (α + β)² - 2αβ

= 8² - 2 × 12

= 64 - 24

= 40

25.Question / प्रश्न

If α and β are the roots of x² − 10x + 16 = 0, find the value of α³β + αβ³.

यदि α और β, x² − 10x + 16 = 0 के मूल हैं, तो α³β + αβ³ का मान ज्ञात कीजिए।

Answer / उत्तर: 1088

Solution / हल:

For x² − 10x + 16 = 0,

α + β = 10

αβ = 16

Now,

α³β + αβ³ = αβ(α² + β²)

α² + β² = (α + β)² − 2αβ

= 10² − 2 × 16

= 100 − 32

= 68

So,

αβ(α² + β²) = 16 × 68

= 1088


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