Answer:
Step-by-step explanation:
Much depends on how accurate an estimate you want.
If "to the nearest hundred" would be acceptable (it's a lot of work),
Round off 542817 to 542820 and 27398 to 2740. Then you'd want to subtract 2740 from 542820. (Again, it's a lot of work.)
Otherwise round off to the nearest thousand: 543000 - 27000.
Or go to the nearest ten thousand: 540,000 - 30,000 = 510,000 (estimate)
