Question 30924
Hello!
The previous answer you got for this question is actually incorrect.

This kind of problems can be solved in the following way. Let's call X to the rate at which welder A does the job per hour. For example, if he could complete the job in 10 hours, then this rate would be 1/10. He completes one tenths of the job per hour. Let's call Y to the same rate for Welder B.

We know that A's rate is 3 times higher than B's:

{{{X = 3Y}}}

We also know thta if they work together, they complete the work in 3 hours. The rate at which they work together is X + Y. If they complete it in 3 hours, then the rate should be 1/3: they complete one third of the job per hour. So we have:

{{{X+Y=1/3}}}

Replacing the 1st equation in the last one:

{{{3Y + Y = 1/3}}}
{{{4Y = 1/3}}}
{{{Y=1/12}}}

So Welder B by himself can complete the job in 12 hours. Since A is 3 times faster, he can complete the job by himself in 4 hours.



I hope this helps!

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