Question 923065
Account for total hours.  You use hours per day and number of days.  You are trying to answer for HOW MANY DAYS.



MORE EXPLANATION:


The problem is a uniform rates type.  The number of dresses to make is not given but you must expect that "a number of dresses" is 1 job to be done.  The basic rule you would use is RT=J for relating rate time and job amounts.  The time T is time in DAYS; the amount of job is an amount J, which you can simply give units as "JOBS", and R is JOBS per DAY.


The best you can really do is to focus on HOURS to do 1 job.
Solve for how many day.


<i>8 hours a day a dressmaker takes 18 days to make a number of dresses.</i>

{{{8(hours/day)*18(days)=8*18*hours}}}, the HOURS to do 1 job.
<i>How long would it take her to make the same number of dresses if she worked 9 hours a day?</i>
LET t be how many days using different number of hours per day.
{{{9(hours/day)*t(days)}}}, the HOURS again to do 1 job, but you do not yet know t.
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{{{highlight(8*18=9*t=1)}}}.