Aptitude - Time and Work - Discussion

How did you get 7/15 after simplifying 7/60 ? Didn't understand the simplification of 7/60 to 7/15 Please explain.

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.

Good explanation but I can't understand how the 1- (7/15) is became 8/15.

Can you explain how is 7/60 came?

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.

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.

How the 0.53333 come 8/15 ?

We have to divide the denominator by its common divisible number and cross multiply it in numerator so you will get 7 then mutilply the highest remainder of lcm with the lowest denominator. You will get answer.

@Jansi.

Both A and B doing the same (one) work, not different work.

I understood upto 7/15. I can't understand how they are telling total work 1. From that they were minusing 7/15 can you explain me.