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Mixing and pouring concrete is complex. The material itself is made from components and recipes that vary with temperature, geography, and handler. Simple field tests are used on fresh batches of concrete to determine the suitability of the batch for the project at hand. The tests involve a device called an Abrams cone, an inverted mold into which fresh concrete is poured. The inverted cone is held tight to the ground to prevent leakage, and the cone is then lifted off the fresh concrete and the behavior of the liberated concrete is observed.

In the case of a flow test, the Abrams cone is lifted and the concrete forms a puddle with an expanding radius. The diameter of the puddle is measured as soon as it stops expanding and the "flow" informs the workers about the readiness of the concrete for use.

In the case of a slump test, the concrete is firmly tamped down within the Abrams cone before the mold is lifted. This concrete does not "flow" as in the flow test; instead, it retains much of its shape and height. The amount of height lost as the concrete settles then is measured. This value is called the "slump".

The following represents paired tests on 103 samples of concrete.

About
Select Option 1%5%10%

of concrete tests result in a slump of less than 5 cm. If a new scatter plot displayed the height of the concrete remaining after the test on the horizontal axis and flow on the vertical axis, the slope of the line of best fit would be
Select Option positivenegativeroughly zero

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