Question 1206703
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A math problem should never be written using any phrase like "... 5 times faster than..." or "... 4 times older than..." or "... 3 times more than...".<br>
Almost certainly, the intended information is that Allen does the job "5 times AS FAST AS" Billy.  In that case, Allen is like 5 Billys, so it's as if 6 Billys are working on the job.  6 Billys will take 1/6 as long as one Billy, so the time it would take to do the job together is 1/6 of 8 hours, or 4/3 hours, or 1 hour and 20 minutes.<br>
However, with the given information that Allen can do the job 5 times FASTER THAN Billy, the conclusion must be that Allen's rate of work is 5 times FASTER THAN Billy's, which would mean that Allen is like one Billy PLUS 5 MORE Billys -- i.e., 1+5 = 6 Billys.  In that case, working together would be like 7 Billys working together, in which case the time required to do the job together would be 1/7 of 8 hours, or 8/7 hours.<br>
Unfortunately, in everyday sloppy English, "3 times more than" and "3 times as much as" are used to mean the same thing; grammatically, they do not.  For the three examples of similar phrases in the first sentence of my response...<br>
5 times FASTER THAN means 1+5=6 times AS FAST AS;
4 times OLDER THAN means 1+4=5 times AS OLD AS;
3 times MORE THAN means 1+3=5 times AS MUCH.<br>
The difference in meaning between "3 times as much as" and "3 times more than" can be seen if we talk in percentages.<br>
Suppose some measurement last year was x. Then...<br>
If this year the measurement is 3 times AS MUCH AS last year, then it is 300% of what it was last year; the measurement now is 3x.
But if this year the measurement is 3 times MORE THAN last year, then it has GROWN BY 300%, which makes the measurement now x+3x = 4x.<br>