Question

5 max has made a mixture of different sizes of rocks for a landscaping project. data about the rocks are in the table below. rock type diameter of rock particles (cm) pea gravel 0.5 pond pebbles 1.0 river rock 2.5 max decides that the river rocks are too large and wants to separate them out. which is the best option? a sift them out with a screen with 1-cm openings. b sift them out with a screen with 2-cm openings. c sift them out with a screen with 3-cm openings. d sift them out with a screen with 4-cm openings.

Explanation:

To separate river rocks (diameter 2.5 cm) while letting pea gravel (0.5 cm) and pond pebbles (1.0 cm) pass, the screen openings must be larger than 1.0 cm (to let pond pebbles through) but smaller than 2.5 cm (to retain river rocks). Let's analyze each option:

• Option A: 1 - cm openings. Pond pebbles (1.0 cm) would not pass (since opening is equal to their diameter, and sifting might require a bit larger to pass easily), so this is not good.
• Option B: 2 - cm openings. Pond pebbles (1.0 cm) and pea gravel (0.5 cm) can pass (2 > 1 and 2>0.5), and river rocks (2.5 cm) are larger than 2 cm, so they will be retained. This works.
• Option C: 3 - cm openings. River rocks (2.5 cm) are smaller than 3 cm, so they will pass through the screen, and we can't separate them.
• Option D: 4 - cm openings. River rocks (2.5 cm) are smaller than 4 cm, so they will pass through the screen, and we can't separate them.

Answer:

B. Sift them out with a screen with 2 - cm openings.