In a school with only sixth and seventh graders 2/5 of the 200 students are seventh graders.

Okay? I'm assumin you want us to find the amount of 6th graders/7th graders.

2/5 of 200 =80.

80 are seventh graders.

200-80=120 sixth graders

1,407.5 hours

step-by-step explanation:

we first convert all the time to hours and then sum them up.

there are 24 hours in 1 day, in 58 days, there are 24 x 58 = 1,392 hours.

there are 60 minutes in 1 hour, thus, 30 minutes will be equivalent to 30 / 60 = 0.5 hours.

therefore, the number of hours it will take mercury to complete a full rotation is 1,392 + 15 + 0.5 = 1,407.5 hours