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Question 231

RRB NTPC 2026• Mathematics• Mathematics

In a fitness park, a straight walking path is divided into three consecutive segments. The lengths of the first and third segments are 18 m and 50 m respectively. If the length of the middle segment is the mean proportional between the other two, what is its length?

  1. AOption (a)

    36 m

  2. BOption (b)

    30 m

  3. COption (c)

    25 m

  4. DOption (d)

    27 m

View answer & explanation

Correct answer

Answer: (b)B.

30 m

Why this answer is correct

Mean proportional = √(a × b) = √(18 × 50) = √900 = 30 m.

Question 232

RRB NTPC 2026• Mathematics• Mathematics

Three automatic doors in a metro station undergo system checks at regular intervals of 14 minutes, 18 minutes, and 21 minutes, respectively. If all three doors are checked together at the start, after how many minutes will they be checked together again for the first time?

  1. AOption (a)

    126 minutes

  2. BOption (b)

    132 minutes

  3. COption (c)

    136 minutes

  4. DOption (d)

    142 minutes

View answer & explanation

Correct answer

Answer: (a)A.

126 minutes

Why this answer is correct

The time they will be checked together again is the LCM of 14, 18, and 21.

14 = 2 × 7

18 = 2 × 32

21 = 3 × 7

LCM = 2 × 32 × 7 = 2 × 9 × 7 = 126 minutes.

Question 233

RRB NTPC 2026• Mathematics• Mathematics

A shopkeeper sells a watch for ₹840 after giving a 30% discount. What was the marked price (in ₹) of the watch?

  1. AOption (a)

    1,100

  2. BOption (b)

    1,050

  3. COption (c)

    1,000

  4. DOption (d)

    1,200

View answer & explanation

Correct answer

Answer: (d)D.

1,200

Why this answer is correct

Selling Price (SP) = Marked Price (MP) × (100 - Discount)%

840 = MP × 70/100

MP = (840 × 100) / 70 = 12 × 100 = ₹1,200.

Question 234

RRB NTPC 2026• Mathematics• Mathematics

A trader sells rice, claiming 1 kg but actually gives x grams. He marks the price 20% above the cost price and gives a 10% discount on the marked price. If his overall profit is 25%, find x.

  1. AOption (a)

    870

  2. BOption (b)

    825

  3. COption (c)

    864

  4. DOption (d)

    856

View answer & explanation

Correct answer

Answer: (c)C.

864

Why this answer is correct

Let CP of 1000g be ₹1000.

MP = 1200.

SP = 1200 × 0.90 = ₹1080.

Overall profit = 25%, so SP / CP_actual = 1.25

1080 / x = 1.25

x = 1080 / 1.25 = 864 grams.

Question 235

RRB NTPC 2026• Mathematics• Mathematics

The price of an article is decreased by 24%, but the daily sale of the article is increased by 33%. Find the net effect on the daily sale receipts.

  1. AOption (a)

    1.08% increase

  2. BOption (b)

    2.16% decrease

  3. COption (c)

    2.16% increase

  4. DOption (d)

    1.08% decrease

View answer & explanation

Correct answer

Answer: (a)A.

1.08% increase

Why this answer is correct

Net effect = a + b + (ab/100)

= -24 + 33 + (-24 × 33 / 100)

= 9 - 7.92 = 1.08% increase.

Question 236

RRB NTPC 2026• Mathematics• Mathematics

40 persons begin to work together on a job. But after some days 10 persons left the work. As a result, the job which should have been completed in 50 days is completed in 60 days. How many days after the commencement of the work did the 10 persons leave?

  1. AOption (a)

    22

  2. BOption (b)

    18

  3. COption (c)

    15

  4. DOption (d)

    20

View answer & explanation

Correct answer

Answer: (d)D.

20

Why this answer is correct

Total work = 40 × 50 = 2000 man-days.

Let the 10 persons leave after 'd' days.

Work done in 'd' days = 40d.

Remaining work done by 30 persons in (60 - d) days = 30(60 - d).

40d + 1800 - 30d = 2000

10d = 200

d = 20 days.

Question 237

RRB NTPC 2026• Mathematics• Mathematics

A cylindrical tank has a radius of 7 m and a height of 11 m. How many litres of water can it hold? (Use π = 22/7)

  1. AOption (a)

    16,74,000

  2. BOption (b)

    16,64,000

  3. COption (c)

    16,94,000

  4. DOption (d)

    16,84,000

View answer & explanation

Correct answer

Answer: (c)C.

16,94,000

Why this answer is correct

Volume = πr2h = (22/7) × 7 × 7 × 11 = 154 × 11 = 1694 m3.

1 m3 = 1000 litres.

Capacity = 1694 × 1000 = 16,94,000 litres.

Question 238

RRB NTPC 2026• Mathematics• Mathematics

Five years ago, the age of Kavita was one-third of the present age of her mother. After 5 years, the sum of their ages will be 75 years. What is Kavita’s present age?

  1. AOption (a)

    21 years

  2. BOption (b)

    22 years

  3. COption (c)

    20 years

  4. DOption (d)

    23 years

View answer & explanation

Correct answer

Answer: (c)C.

20 years

Why this answer is correct

Let Kavita's present age be K and Mother's be M.

K - 5 = M/3 => M = 3K - 15.

(K + 5) + (M + 5) = 75 => K + M = 65.

K + (3K - 15) = 65

4K = 80

K = 20 years.

Question 239

RRB NTPC 2026• Mathematics• Mathematics

Aman and Raj invested ₹12,000 and ₹18,000, respectively, in a business. After one year, they earned a profit of ₹15,000. How much profit will each get?

  1. AOption (a)

    Aman: ₹7,500, Raj: ₹7,500

  2. BOption (b)

    Aman: ₹6,000, Raj: ₹9,000

  3. COption (c)

    Aman: ₹8,000, Raj: ₹7,000

  4. DOption (d)

    Aman: ₹5,000, Raj: ₹10,000

View answer & explanation

Correct answer

Answer: (b)B.

Aman: ₹6,000, Raj: ₹9,000

Why this answer is correct

Ratio of investment = 12000 : 18000 = 2 : 3.

Aman's profit = (2/5) × 15000 = ₹6,000.

Raj's profit = (3/5) × 15000 = ₹9,000.

Question 240

RRB NTPC 2026• Mathematics• Mathematics

Find the mode of the following distribution:

Class5-1515-2525-3535-45
Frequency6141812
  1. AOption (a)

    26

  2. BOption (b)

    29

  3. COption (c)

    28

  4. DOption (d)

    30

View answer & explanation

Correct answer

Answer: (b)B.

29

Why this answer is correct

Modal class is 25-35 (highest frequency 18).

L = 25, f1 = 18, f0 = 14, f2 = 12, h = 10.

Mode = L + [(f1 - f0) / (2f1 - f0 - f2)] × h

Mode = 25 + [(18 - 14) / (36 - 14 - 12)] × 10

Mode = 25 + [4 / 10] × 10 = 29.

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