The graph below shows the rate of natural gas usage (in therms per day) in one household for a 30 - day period. Estimate the total number of therms used during this period. Use left endpoints and rectangles with widths of 3 days.

Question

View graph at:

postimg.o r g/image/61nw3co3r/

Answer 1

They conveniently have the x-axis divided into 3-day periods.

For the first rectangle, the height is 3, so its area is 3x3 = 9

The next rectangle has height 4, and so on.

Then just add up all the areas.

Answer 2

I'm lost. I think am adding wrong.

Answer 3

so, what are you adding? Just look at the height of the left side of each rectangle in the picture, and multiply by the width, which is always 3.

Answer 4

i came up with 165.