Hello, slendersnake!

1. A 100-ft oil is to be drilled. The cost of drilling the first foot is $10.00.

The cost for drilling each additional foot is $0.50 more than that of preceding foot.

Find the cost of drilling the entire 100 ft.

This is an Arithmetic Series with:

. . first term , common difference ,

Therefore: .

. . The cost is: .

After the 1st replacement, the amount of water is: . gallons.2. A tank contains 20 gallons of water.

One half of theand replaced with antifreeze.wateris removed

This process is continued eight times.

How much water remains in the tank after these eight replacements process?

After the 2nd replacement, the amount of water is: . gallons.

After the 3rd replacement, the amount of water is: . gallons.

. . . . . etc. . . .

After the 8th replacement, the amount of water is: . gallons.

And: .