Arithmetic Aptitude :: Chain Rule

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If 7 spiders make 7 webs in 7 days, then 1 spider will make 1 web in how many days?


A1

B7/2

C7

D49

Answer: Option C

Explanation:

Let the required number days be x.

Less spiders, More days (Indirect Proportion)
Less webs, Less days (Direct Proportion)

Spiders 1 : 7 }
> :: 7 : x
Webs 7 : 1 }
1 x 7 x x = 7 x 1 x 7
=> x = 7

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An industrial loom weaves 0.128 metres of cloth every second. Approximately, how many seconds will it take for the loom to weave 25 metre of cloth ?


A194 seconds

B195 seconds

C196 seconds

D197 seconds

Answer: Option B

Explanation:

Lets assume the time required to weave 25 meters = x sec.
Rule: More cloth means More time (Direct Proportion)

=> 0.128:1::25:x
=>x=[(25*1)/0.128]
=>x=195.31
So time needed ~195 seconds

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If 16 toys cost 240, then what do 40 toys cost ?


ARs. 600

B2. Rs. 620

CRs. 640

DRs. 660

Answer: Option A

Explanation:

Lets assume 40 toys cost is Rs.x

Toys cost
---------------------
16(d) 240(d)
40 x

=> 40/16 = x/240
=> x = 40/16 * 240
=> x = 600

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If the price of 23 toys is 276, then what will the price of 12 toys ?


A144

B148

C156

D186

Answer: Option A

Explanation:

Lets assume 12 toys price is Rs.x

Toys Price
---------------------
23(d) 276(d)
12 x

=> 12/23 = x/276
=> x = 12/23 * 276
=> x = 144.

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A flagstaff 17.5 metre high casts a shadow of length 40.25 metre. The height of building, which casts a shadow of length 28.75 metre under similar conditions will be :


A12 metre

B12.5 metre

C13.5 metre

D14 metre

Answer: Option B

Explanation:

Lets assume x meter is building height.

flags shadow
---------------------
17.5 (d) 40.25 (d)
x 28.75

=> x/17.5 = 28.75/40.25
=>x = (28.75 * 17.5)/40.25
=> x = 12.5 meters.

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In a hostel, Food was available for 2000 students for 54 days, but after 15 days more students joined hostel and food lasts only for 20 more days. Determine how many students came in hostel ?


A1650

B1700

C1900

D2100

Answer: Option C

Explanation:

food is there for 54 days for 2000 students,
But after 15 days, remaining food was sufficient for 2000 students for 39 days only ( as 54-15 = 39 )
Let x number of students came in hostel after 15 days,
=> Total number of students after 15 days = 2000 + x
=> Remaining food was enough for (2000 + x) students for 20 days

Note: (u) means up arrow and (d) means down arrow.

students days
------------------
200(u) 20(u)
(200+x) 39

=> 200/(200/x)= 20/39
=> 2000*39 = (2000 + x) * 20
=> 3900 = 2000 + x-10
=> x = 1900

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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?


A5

B6

C7

D7 1/2

Answer: Option B

Explanation:

Lets assume x days required to finish the remaining job.

Note: (u) means up arrow and (d) means down arrow.

Job days
----------------
5/8(d) 10(d)
3/8 x

=> (3/8)/(5/8) = x/10
=> 3/5 = x/10
=> x = 6 days.

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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


A18 days

B21 days

C24 days

D30 days

Answer: Option B

Explanation:

(2 * 14) men +(7 * 14)boys=(3 * 11)men +(8 * 11)boys

<=> 5 men= 10 boys <=> 1 man = 2 boys

so (2 men + 7 boys) = (2 * 2 + 7) boys = 11 boys

=> ( 8 men + 6 boys) = (8 * 2 +6) boys = 22 boys.
Lets assume x days required.

Note: (u) means up arrow and (d) means down arrow.

boys work days
------------------
11(u) 1(d) 14(d)
22 3 x

(11/22 * 3/1) = x/14
=> x = (11/22 * 3* 14)
=> x = 21 days.

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3 pumps working 8 hours a day, can empty a tank in 2 days. How many hours a day must 4 pumps work to empty the tank in 1 day?


A9

B10

C11

D12

Answer: Option D

Explanation:

Lets assume x hrs a days required to empty tank.

Note: (u) means up arrow and (d) means down arrow.

pumps hrs days
-------------------------
3(u) 8(d) 2(u)
4 x 1

(3/4 * 2/1) = x/8
=> x = (3/4 * 2 * 8)
=> x = 12 hrs.

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36 men can complete a piece of work in 18 days. In how many days will 27 men complete the same work ?


A24 days

B28 days

C34 days

D35 days

Answer: Option A

Explanation:

Lets assume x day need to complete the work.

Note: (u) means up arrow and (d) means down arrow.

men work days
---------------------
36(u) 1(d) 18(d)
27 1 x

(36/27 * 1) = x/18
=> x = 36/27 * 18 = 24 days.

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