Mr. Boone can do one job in ten days. So after 3 days, he has already done 3/10ths of the job. Working together, it takes 4 days to finish the remaining 7/10ths. So we subtract the two rates to find the helper's work rate:

So in one day, the helper can complete 3/40ths of a job. To find the number of days it would take to complete an entire job, take the reciprocal:

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