The correct answer is 3780 bolts
Explanation:
In one hour the machine can make either 500 nuts or 840. Now, if the machine first made 750 nuts, this means the machine worked 1.5 hours. You can know this using the rule of three:
500 nuts (a) = 1 hour (b)
750 nuts (c) = x (time spent to make 750 nuts)
x = 750 x 1 / 500
x = 1.5
Note: In a rule of three you find the fourth unknown value if you multiply value b by c and divide it by the value a.
According to this, the machine worked 1.5 hours making nuts, and if the machine started at 2 pm, this means the machine ended making nuts at 3.30 pm as 2 pm + 1.5 hours = 3:30 pm (2 + 1.5 = 3.5 ). Now you know the machine made bolts from 3: 30 pm to 8:00 p.m. This means the time the machine made bolts was 4 and a half hours or 4.5 hours (8 - 3.5 = 4.5). At this point, the only missing step is to multiply the time 4.5 hours by the number of bolts the machine makes each hour 840 and this is equivalent to 3780 bolts (840 x 4.5 = 3780).
