The measurements below were made on four different balances: i. 7.5 g
ii. 7.33 g
iii. 7.5201g
iv. 7.490

A student takes a reading from a balance where the display fluctuates between 7.51 g and 7.55 g. Which of the four balances above was used?

a. iv
b. iii
c. i
d. ii

d. ii.

Explanation:

Hello!

In this case, according to the displayed decimal placed by each balance, we can notice that:

i. Displays 1 decimal place.

ii. Displays 2 decimal places.

iii. Displays 4 decimal places.

iv. Displays 3 decimal places.

Thus, since the measured-out masses have two decimal places each, we infer that the used balance was d. ii as it displays two decimal places.

Best regards!

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.