Practise Quiz - Compression Rate


Hi coach Garric, I am lost on the logic of determining the correct sample from this question. To me, 20018 seems not correct, because for more than 30 days, the test result is still under the compression rate. Of course eventually, concrete will reach that compression, but this is not what it was specified.

The other options seem possible in their own ways. e.g. 20014 surpassed the compression rate way earlier, it is probably not a good thing, but it meets the requirement.

20015 and 20016 are reasonably at their curing rate.

20017, 20019 and 20020 are also appropriate as they passed the min. compression rate after 27 days.

20018 is the first option that I ruled out right away, but it is the only exemption that appears different from the rest. Perhaps you could help shed light on elaborating why it is the correct answer. Or explain why the others are wrong.

thanks a lot


@vincent.c.lee great question! When determining what the question is asking, we need to find out which samples were tested at a minimum of 28 days after the cast date, therefore, we have to rule out 20014, 2015, and 2016 because these are all fewer than 28 days. The next requirement is that we need to have a minimum of 6,000 PSI; 20017, 20019, and 20020 all exceed the 6,000 PSI requirement - which is good! This then leaves the only option as the 20018 because it had successfully reached the 28 day requirement, but then broke under the 6,000 PSI requirements thus leaving 20018 as the correct answer!

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