Question 1198709
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You have two different responses that show two different ways to solve "working together" problems like this.  Here is a third method.<br>
Consider the least common multiple of the two given times, which is 3 hours.<br>
The two reapers together harvest the field in 1 hour; so in 3 hours, the two reapers together could harvest a field that size 3/1 = 3 times.
The newer reaper can harvest the field in 1.5 hours; so in 3 hours, the newer reaper could harvest a field that size 3/1.5 = 2 times.
So in 3 hours, the older reaper could harvest a field that size 3-2 = 1 time.<br>
So it would take the older reaper 3 hours to harvest the field.<br>