Aptitude - Time and Work - Discussion
Discussion Forum : Time and Work - General Questions (Q.No. 24)
24.
A works twice as fast as B. If B can complete a work in 12 days independently, the number of days in which A and B can together finish the work in :
Answer: Option
Explanation:
Ratio of rates of working of A and B = 2 : 1.
So, ratio of times taken = 1 : 2.
| B's 1 day's work = | 1 | . |
| 12 |
 A's 1 day's work = |
1 | ; (2 times of B's work) |
| 6 |
| (A + B)'s 1 day's work = |  |
1 | + | 1 |  |
= | 3 | = | 1 | . |
| 6 | 12 | 12 | 4 |
So, A and B together can finish the work in 4 days.
Discussion:
28 comments Page 1 of 3.
Paandu said:
1 decade ago
Why we are ratio this problem and ratio of times taken = 1:2 ?
Ghousia said:
1 decade ago
simplest method:
A is twice of B then B=2A
B completes work in=12
then 2A=12=>A=6
A's 1 day work=1/6, B's 1 day work=1/12
(A+B)'s 1 day work=(1/6+1/12)=3/12=1/4
now (A+B) together finish work in 4days
A is twice of B then B=2A
B completes work in=12
then 2A=12=>A=6
A's 1 day work=1/6, B's 1 day work=1/12
(A+B)'s 1 day work=(1/6+1/12)=3/12=1/4
now (A+B) together finish work in 4days
Arun Pandian said:
1 decade ago
SHORT CUT METHOD:
let x=2(bcz A is twice as fast as B)
n=12(bcz B completes the work in 12 days)
use the formula:A&B together do the work in p days as follows
p=n/x+1
=12/3
=4days
let x=2(bcz A is twice as fast as B)
n=12(bcz B completes the work in 12 days)
use the formula:A&B together do the work in p days as follows
p=n/x+1
=12/3
=4days
Umeshprasad said:
1 decade ago
Let A's 1 day work is x
B's 1 day work is 1/12
from question a is twice as fast as B
so A=2B------------(1)
x=2*1/12=>1/6
which is one day work of A
combine one day work of A and B is (1/6)+(1/12)
which will give u 1/4
so the entire work they will finish in 4 day.
B's 1 day work is 1/12
from question a is twice as fast as B
so A=2B------------(1)
x=2*1/12=>1/6
which is one day work of A
combine one day work of A and B is (1/6)+(1/12)
which will give u 1/4
so the entire work they will finish in 4 day.
Deepa said:
1 decade ago
B'S one day work=1/12
A'S one day work=2(1/12)=1/6
(A+B) one day work=(1/12)+(1/6)=1/4
hence A and B together complete the work in 4 days
A'S one day work=2(1/12)=1/6
(A+B) one day work=(1/12)+(1/6)=1/4
hence A and B together complete the work in 4 days
Kapil said:
1 decade ago
Simple : A 's twice ie Half of B. . .So B is 1/12 thn Frm tis A is 1/12. . .thn A+B we get t Ans. . .
Omkar said:
1 decade ago
A = 2B.
Hence,
A+B = 2B + B
i.e. as good as three Bs working together.
B completes in 12 Days,
3B will take 1/3rd of the time i.e. 12/3 = 4.
Hence,
A+B = 2B + B
i.e. as good as three Bs working together.
B completes in 12 Days,
3B will take 1/3rd of the time i.e. 12/3 = 4.
Atul1487 said:
1 decade ago
Simple method without any rubbish ratio.
Suppose B completes 1 work in x days.
So B completed work in 1 day = 1/x.............1.
Now A completes 1 work = x/2 (Cz A is twice faster than B).
So A completed work in 1 day = 2/x.............2.
Together their Work = 1/x + 2 /x.
Given x = 12.
So,
Together their Work = 1/12 + 2 /12.
== 1/12 + 1/6.
==1/4 or 4 days.
No ratio - nothing complicated.
Suppose B completes 1 work in x days.
So B completed work in 1 day = 1/x.............1.
Now A completes 1 work = x/2 (Cz A is twice faster than B).
So A completed work in 1 day = 2/x.............2.
Together their Work = 1/x + 2 /x.
Given x = 12.
So,
Together their Work = 1/12 + 2 /12.
== 1/12 + 1/6.
==1/4 or 4 days.
No ratio - nothing complicated.
Swati said:
1 decade ago
SHORTCUT:
A is twice efficient as B that means If B takes 12 days then A will take 6 days.
Now both are working together. So definitely together they'll take less than 6 days. ONLY option less than 6 days is Option A i.e. 4 days.
A is twice efficient as B that means If B takes 12 days then A will take 6 days.
Now both are working together. So definitely together they'll take less than 6 days. ONLY option less than 6 days is Option A i.e. 4 days.
Aravind_appu said:
1 decade ago
A = 2b------(1).
B = 1/12------(2).
1 sub in 2.
A = 2(1/12).
A = 1/6.
Total work is done TH = A+B.
TH = (1/6+1/12).
= (12+6)/(6*12).
= (18/72).
= 1/4.
= 4 day exactly.
B = 1/12------(2).
1 sub in 2.
A = 2(1/12).
A = 1/6.
Total work is done TH = A+B.
TH = (1/6+1/12).
= (12+6)/(6*12).
= (18/72).
= 1/4.
= 4 day exactly.
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