word problems redone. are these correct. Thanks!

K

kyl367

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Feb 17, 2010
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1. How many cubic yards of concrete are needed to pour a concrete slab 24 feet long, 14 feet wide, and 8 inches thick?
V=Ah
A=LW
A=24 * 14= 336 ft^2
V= 336 * h
V= 336ft^2 * .67 ft =225.12 ft^3
225.12 cubic feet divided by 27= 8.34 cubic yards
2. How many cubic feet of concrete are needed to pour 4 cylindrical pillars 6 feet high with a diameter of 10 inches?
(pi) (r^2) (h)
3.14 X 25 X 72 in =5652 in^2
5652 X 4=22608 in^2
22608 / 1728= 13.08 cubic feet
 
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Your reasoning looks good.

However, if you want to report these volumes to the nearest 1/100th of a cubic unit, your values are not properly rounded.

In the first exercise, by rounding your value for 2/3rds of a foot to 0.67, you introduced "round-off error". At a minimum, you need to use 0.667 feet for 8 inches.

Rounded to the nearest 1/100th cubic unit, exercise (1) is 8.30 cubic yards.

Likewise, your approximation for Pi, in the second exercise, does not have enough precision. Do you know? Bridges have collapsed under the weight of trucks because some engineering firms did not use enough decimal places for Pi.

Rounded to the nearest 1/100th cubic unit, exercise (2) is 13.09 cubic feet.

I suggest that you not round intermediate results. Since you're using a calculator, anyway, just let it carry all 8 decimal places (or whatever the number that your particular calculator holds) from one calculation to the next, and wait until the very end to round the final answer.

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You're welcome. I just noticed that you had previously started a separate discussion, for these exercises.

In the future, when you have something additional to post on an existing thread, please append your post, instead of starting a "new topic".

Otherwise, we'll end up having people in multiple locations on the boards talking to you about the same exercise(s), and it won't be clear what all has been said or done, to date.

In other words, it's better to have everybody involved on the "same page".

Thank you. 8-)

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