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:
347 comments Page 25 of 35.
Prasad said:
1 decade ago
(1/15+1/20) = 7/60.
Explanation:
15 = 5*3.
20 = 5*4.
Here the common nums are 3,4,5.
3*4*5 = 60.
60/15 = 4.
60/20 = 3.
(3/60+4/60) = 7/60.
Explanation:
15 = 5*3.
20 = 5*4.
Here the common nums are 3,4,5.
3*4*5 = 60.
60/15 = 4.
60/20 = 3.
(3/60+4/60) = 7/60.
Mahesh Gehlot said:
1 decade ago
7/60 is the total work done by A and B in day 1.
Therefore for 4 days we will calculate as below.
7/60 *4 means when its multiplication we will divide.
ie. 4/15 = 60 and we need to keep 7 integer as it was.
Therefore we get 7/15.
I don't know, Hope you'll understand this.
A simple logic when its + or - we will cross multiply
And when its * we will divide.
Thanks.
Therefore for 4 days we will calculate as below.
7/60 *4 means when its multiplication we will divide.
ie. 4/15 = 60 and we need to keep 7 integer as it was.
Therefore we get 7/15.
I don't know, Hope you'll understand this.
A simple logic when its + or - we will cross multiply
And when its * we will divide.
Thanks.
Latha said:
1 decade ago
Work done=>4*(1/15)+4*(1/20) = 7/15.
Remaining work = 1-7/15.
= 8/15.
Option D.
Remaining work = 1-7/15.
= 8/15.
Option D.
Nishi said:
1 decade ago
How did you get 7/15 after simplifying 7/60 ? Didn't understand the simplification of 7/60 to 7/15 Please explain.
Ellaiah Malli said:
1 decade ago
For 7/60.
It is necessary to add both 1/15 and 1/20.
But the denominators are different.
So first we equals the denominators by multiplying with.
Two different alternatives.
i.e.
1/15*4/4.
Because whenever we want to gave an alternative for multiplying.
It should applicable to both numerator and denominator.
That's why we use 4/4 for 1/15.
As the same way for 1/20.
We multiplying with 3.
i.e.
1/20*3/3.
Why I'm particularly take 4/4 and 3/3 particularly is.
This is the minimum stage to equal both denominators, understand.
Now it is easy to add.
It is necessary to add both 1/15 and 1/20.
But the denominators are different.
So first we equals the denominators by multiplying with.
Two different alternatives.
i.e.
1/15*4/4.
Because whenever we want to gave an alternative for multiplying.
It should applicable to both numerator and denominator.
That's why we use 4/4 for 1/15.
As the same way for 1/20.
We multiplying with 3.
i.e.
1/20*3/3.
Why I'm particularly take 4/4 and 3/3 particularly is.
This is the minimum stage to equal both denominators, understand.
Now it is easy to add.
Rajendra said:
1 decade ago
Good explanation but I can't understand how the 1- (7/15) is became 8/15.
Shamanth Kumar Sm said:
1 decade ago
Can you explain how is 7/60 came?
Haphyz said:
1 decade ago
When dealing with addition or subtraction of fractions you consider the denominators i.e
15&20 and then you find the L.C.M which is 60 or multiply them together.
15*20 = 300 so,
(1/15 + 1/20)/300 = (20 + 15)/300.
=25/300 reduce to the lowest term and you get 7/60.
This 7/60 is the amount of work A & B will complete in one day.
Hence for 4 days we have;
7/60 * 4 = 7/15 of the total work.
Since we don't know the real value of the total work we then assume total work to be done to be 1.
Therefore,
Remaining work left will be,
1- (work done)
1-7/15 ; the denominator here is 15 & 1 (since 1 =1/1).
Do the math and you get our final answer to be 8/15.
NOTE !
If you are subtracting a fraction from a whole number, just multiply the denominator by the whole number and then subtract from the numerator. The same rule applies for addition.
15&20 and then you find the L.C.M which is 60 or multiply them together.
15*20 = 300 so,
(1/15 + 1/20)/300 = (20 + 15)/300.
=25/300 reduce to the lowest term and you get 7/60.
This 7/60 is the amount of work A & B will complete in one day.
Hence for 4 days we have;
7/60 * 4 = 7/15 of the total work.
Since we don't know the real value of the total work we then assume total work to be done to be 1.
Therefore,
Remaining work left will be,
1- (work done)
1-7/15 ; the denominator here is 15 & 1 (since 1 =1/1).
Do the math and you get our final answer to be 8/15.
NOTE !
If you are subtracting a fraction from a whole number, just multiply the denominator by the whole number and then subtract from the numerator. The same rule applies for addition.
(2)
Shrikant said:
1 decade ago
a/b + c/d.
= a*d/b*d + c*b/b*d.
= ad+cb/b*d.
Maths rule if denominator not equal if equal directly cross multiplication.
= a*d/b*d + c*b/b*d.
= ad+cb/b*d.
Maths rule if denominator not equal if equal directly cross multiplication.
Thiyagu said:
1 decade ago
How the 0.53333 come 8/15 ?
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