Chain Rule problems
- 1. Running at the same constant rate, 6 identical machines can produce a total of 270 bottles per minute. At this rate, how many bottles could 10 such machines produce in 4 minutes?
Options- A. 648
- B. 1800
- C. 2700
- D. 10800 Discuss
Correct Answer: 1800
Explanation:
Let the required number of bottles be x
More machines, More bottles (Direct Proportion)
More minutes, More bottles (Direct Proportion)
| Machines | 6 | : | 10 | ] | :: 270 : x |
| Time (in minutes) | 1 | : | 4 |
∴ 6 x 1 x x = 10 x 4 x 270
| ⟹ x = | (10 x 4 x 270) |
| (6) |
⟹ x = 1800.
- 2. If a quarter kg of potato costs 60 paise, how many paise will 200 gm cost?
Options- A. 48 paise
- B. 54 paise
- C. 56 paise
- D. 72 paise Discuss
Correct Answer: 48 paise
Explanation:
Let the required weight be x kg.
Less weight, Less cost (Direct Proportion)
∴ 250 : 200 :: 60 : x ⟺ 250 x x = (200 x 60)
| ⟹ x= | (200 x 60) |
| 250 |
⟹ x = 48.
- 3. A fort had provision of food for 150 men for 45 days. After 10 days, 25 men left the fort. The number of days for which the remaining food will last, is:
Options- A. 29 1⁄5
- B. 37 1⁄4
- C. 42
- D. 54 Discuss
Correct Answer: 42
Explanation:
After 10 days : 150 men had food for 35 days.
Suppose 125 men had food for x days.
Now, Less men, More days (Indirect Proportion)
∴ 125 : 150 :: 35 : x ⟺ 125 x x = 150 x 35
| ⟹ x = | 150 x 35 |
| 125 |
⟹ x = 42.
- 4. A man completes 5⁄8 of a job in 10 days. At this rate, how many more days will it takes him to finish the job?
Options- A. 5
- B. 6
- C. 7
- D. 7 1⁄2 Discuss
Correct Answer: 6
Explanation:
| Work done = | 5 |
| 8 |
| Balance work = | ❨ | 1 - | 5 | ❩ | = | 3 |
| 8 | 8 |
Let the required number of days be x.
| Then, | 5 | : | 3 | = :: 10 : x | ⟺ | 5 | x x = | 3 | x 10 |
| 8 | 8 | 8 | 8 |
| ⟹ x = | ❨ | 3 | x 10 x | 8 | ❩ |
| 8 | 5 |
⟹ x = 6.
- 5. 39 persons can repair a road in 12 days, working 5 hours a day. In how many days will 30 persons, working 6 hours a day, complete the work?
Options- A. 10
- B. 13
- C. 14
- D. 15 Discuss
Correct Answer: 13
Explanation:
Let the required number of days be x
Less persons, More days (Indirect Proportion)
More working hours per day, Less days (Indirect Proportion)
| Persons | 30 | : | 39 | ] | :: 12 : x |
| Working hours/day | 6 | : | 5 |
∴ 30 x 6 x x = 39 x 5 x 12
| ⟹ x = | (39 x 5 x 12) |
| (30 x 6) |
⟹ x = 13.
- 6. If 20 men can build a wall 56 meters long in 6 days , what length of a similar wall can be built by 35 men in 3 days?
Options- A. 46
- B. 47
- C. 48
- D. 49 Discuss
Correct Answer: 49
Explanation:
Let the required length be x meters
More men, More length built (Direct proportion)
Less days, Less length built (Direct Proportion)
=> (20 x 6 x X)=(35 x 3 x 56)
=> x = 49
Hence, the required length is 49 m.
- 7. A certain number of men can finish a piece of work in 100 days. If there were 10 men less, it would take 10 days more for the work to be finished. How many men were there originally?
Options- A. 75
- B. 82
- C. 100
- D. 110 Discuss
Correct Answer: 110
Explanation:
Originally let there be x men.
Less men, More days (Indirect Proportion)
Therefore, (x-10) : x :: 100 :110
=> (x - 10) * 110 = x * 100 => x= 110
- 8. If 36 men can do a piece of work in 25 hours, in how mwny hours will15 men do it?
Options- A. 40
- B. 50
- C. 60
- D. 70 Discuss
Correct Answer: 60
Explanation:
Let the required no of hours be x. Then
Less men , More hours (Indirct Proportion)
Therefore, 15:36 ::25:x
=> (15 x X)=(36 x 25) => x = 60
Hence, 15 men can do it in 60 hours.
- 9. 2 men and 7 boys can do a piece of work in 14 days; 3 men and 8 boys can do the same in 11 days. Then, 8 men and 6 boys can do three times the amount of this work in
Options- A. 18 days
- B. 21 days
- C. 24 days
- D. 30 days Discuss
Correct Answer: 21 days
Explanation:
(2 x 14) men +(7 x 14) boys = (3 x 11) men + (8 x 11) boys
=>5 men= 10 boys => 1man= 2 boys
Therefore, (2 men+ 7 boys) = (2 x 2 +7) boys = 11 boys
( 8 men + 6 boys) = (8 x 2 +6) boys = 22 boys.
Let the required number of days be x.
More boys , Less days (Indirect proportion)
More work , More days (Direct proportion)
Therefore, (22 * 1 * x) = (11 * 3 * 14)
=> x = 21
Hence, the required number of days = 21
- 10. If 7 spiders make 7 webs in 7 days, then 1 spider will make 1 web in how many days?
Options- A. 1
- B. 3
- C. 7
- D. 14 Discuss
Correct Answer: 7
Explanation:
Let the required number days be x.
Less spiders, More days (Indirect Proportion)
Less webs, Less days (Direct Proportion)
=> 1 * 7 * x = 7 * 1 * 7
=> x= 7
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