Aptitude - Pipes and Cistern - Discussion

1/5 is taken wrt to 1 hr but not A B C they are taken as A, 2A, 4A which has to to be taken wrt 1hr but in equation how are they equating A, 2A,4A to 1/5 in an equation. if we want to solve an equation it should be write to 1 hr only.

As per the question we can solve as:
c=2b;-------->1.
b=2a;-------->2.

Also a+b+c=1/5(work done in 1 hour by a,b,c)--------?3.

Now substitute the value of c=2b and b=2a in 3.
So eqn.3 becomes a+2a+2b = 1/5.

Again substitute b=2a in place of b.
So eqn becomes 3a+4a = 1/5.

So solving we get the value of a = 1/35.
So that is d work done in 1 hr.
So total work done = 35.

1/x+2/x+4/x = 7/x. How it will possible?

C is twice fast as B.
B is twice fast as A.
So, speed here If A = x, B = 2x, C = 4x.
Is speed increases time decrease. As we know from the above speeds we can get the value of time. B is twice fast as A. It mean just think speed multiplies. But time it should be divided.

So, If A takes x hour then B takes less time. It mean x/2. Similarly, C is twice fast as B. It mean if B takes x/2hr. Then C takes less than B as x/4.

So finally A takes x hr, B takes x/2 hr, and C takes x/4 hr.

Why not it is 1/x + 1/2x + 1/4x = 1/5?

In some problem, they subtracted the values and here it is dividing. Can you please explain in detail?

ABC-A -B-C
5-35
7-1-2-4

Because 7 * 5 = 35 means that 1 * 35 = 35 answer, if we want to find B means 2 * 35 = 70h.

Given: B = 2 times of A.
C = 2 times of B.

Assume A = 1, so B= 2(A)= 2 and C= 2(B)= 4.
Total = 1 + 2 + 4 =7.
Now multiply it 7*5.
Answer = 35.

Don't be confuse.

A x hours and B is twice fast it means is that B is faster than A.

So B is x /2. By this way B is twice faster than A.

Hi friends please tell how 1/5 is come here.