Aptitude - Time and Work - Discussion
Discussion Forum : Time and Work - General Questions (Q.No. 1)
1.
A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :
Answer: Option
Explanation:
| A's 1 day's work = | 1 | ; |
| 15 |
| B's 1 day's work = | 1 | ; |
| 20 |
| (A + B)'s 1 day's work = |  |
1 | + | 1 |  |
= | 7 | . |
| 15 | 20 | 60 |
| (A + B)'s 4 day's work = | |
7 | x 4 | |
= | 7 | . |
| 60 | 15 |
| Therefore, Remaining work = | |
1 - | 7 | |
= | 8 | . |
| 15 | 15 |
Discussion:
344 comments Page 9 of 35.
Carlo said:
1 decade ago
4(1/15 + 1/20) + X = 1.
X = 8/15.
X = 8/15.
Kumar said:
1 decade ago
Why are we subtracting 7/15 from 1 ?
Why not any other number?
Why not any other number?
Tinu said:
1 decade ago
Because a work is calculated as 1.
If any value coming under fraction it comes between 0 to 1 so only.
Like 15/15 = 1.
Likewise Here we have 7/15 only, we need to know the remaining.
15/15-7/15 = 15-7/15 = 8/15.
If any value coming under fraction it comes between 0 to 1 so only.
Like 15/15 = 1.
Likewise Here we have 7/15 only, we need to know the remaining.
15/15-7/15 = 15-7/15 = 8/15.
DEEPAK said:
1 decade ago
A = 20, B = 15.
TOTAL WORK FOR ONE DAYS = 7/60.
4 DAYS = 7/15.
Remaining work = 8/15.
TOTAL WORK FOR ONE DAYS = 7/60.
4 DAYS = 7/15.
Remaining work = 8/15.
Mukesh Mishra said:
1 decade ago
A's 1 day work=1/15; B's 1 day work = 1/20.
OK. Then we calculate how much A + B can do in 1 day.
i.e. 1/15 + 1/20 ( in fraction if denominator is different first we find the l.c.m of denominator). So we calculate the l.c.m of 15 and 20 i.e 60(15 and 20 is divided by 5 we get the answer 3 and 4 so we find l.c.m by multiplying 5*3*4=60). 1/15*60+1/20*60 = 4+3/60 = 7/60.
If A and B do work in 4 days = 7/60*4 = 7/15.
Remaining work = 1-7/15 = 8/15 [ (15*1-7)/15 = 8/15.
OK. Then we calculate how much A + B can do in 1 day.
i.e. 1/15 + 1/20 ( in fraction if denominator is different first we find the l.c.m of denominator). So we calculate the l.c.m of 15 and 20 i.e 60(15 and 20 is divided by 5 we get the answer 3 and 4 so we find l.c.m by multiplying 5*3*4=60). 1/15*60+1/20*60 = 4+3/60 = 7/60.
If A and B do work in 4 days = 7/60*4 = 7/15.
Remaining work = 1-7/15 = 8/15 [ (15*1-7)/15 = 8/15.
Geek said:
1 decade ago
1-((1/20+1/15)*4)==>1-7/15==>8/15.
This is easy method, I think. If any other easy method please give me.
This is easy method, I think. If any other easy method please give me.
Sowmi said:
1 decade ago
Why the value of b had multiplied but in final there is a subtraction is held?
Kiran said:
1 decade ago
Can you explain How you got = (1/15+1/20) = 7/60?
Shiva said:
1 decade ago
@Kiran.
(1/15+1/20) = (20+15)/300 //This get by cross multiplication.
= 35/300.
= 7/60.
I think your doubt is clear now.
(1/15+1/20) = (20+15)/300 //This get by cross multiplication.
= 35/300.
= 7/60.
I think your doubt is clear now.
Viky said:
1 decade ago
I'm confused, can anybody tell me how 7/60 came?
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