The amount of asphalt needed to be placed on the driveway is approximately 128.85 tons.
To calculate the amount of asphalt needed, we need to find the volume of the asphalt layer. First, convert the measurements to the same unit. Since 1 foot is equal to 12 inches, the length of the driveway becomes 835 feet * 12 inches/foot = 10,020 inches. Similarly, the width is 20 feet * 12 inches/foot = 240 inches.
Next, convert the thickness of the asphalt to inches. 2 ½ inches is equal to 2.5 inches. Now, we multiply the length, width, and thickness to find the volume. Volume = 10,020 inches * 240 inches * 2.5 inches = 6,012,000 cubic inches.
Lastly, we need to convert the volume from cubic inches to tons. The conversion factor is 1 ton = 46,656 cubic inches. Therefore, Tons = 6,012,000 cubic inches / 46,656 cubic inches/ton ≈ 128.85 tons.