Errors: Both of your upper bounds are wrong
You subtracted the upper bound from the upper bound
Step-by-step explanation:
605 kg to the nearest 5 kg
lower bound is 602.5 (because it rounds up to 605)
upper bound is 607.4 (because it rounds down to 605)
Note: 607.5 would round up to 610
78 kg rounded to the nearest 1 kg
lower bound is 77.5 (because it rounds up to 78)
upper bound is 78.4 (because it rounds down to 78)
Note: 78.5 would round up to 79
Upper Bound - Lower bound is the maximum weight remaining on the elevator
607.4 - 77.5 = 529.9
529.9 ≤ 530 so YES the elevator is safe.
