Why Do Some Odd Numbers Fail to Be Prime?

[vroman]

For some reason, my answers to these questions are wrong, but I don't understand which ones and why, please help:

A)The speed of an accelerated body changes with time...False
B)THe velocity of an accelerated body changes with time...True
C)The words motion and acceleration can be used interchangeably...False
D)The position of a body in motion changes with time...False
E)The acceleration of a body with zero speed is zero...False
F)Motion and acceleration are not the same quantity...True

 

[jdavel]

vroman,

They're all right except one. That should help!

 

[vroman]

Thanks, I figured it out!

 

[Curious3141]

For some reason, my answers to these questions are wrong, but I don't understand which ones and why, please help:

A)The speed of an accelerated body changes with time...False
B)THe velocity of an accelerated body changes with time...True
C)The words motion and acceleration can be used interchangeably...False
D)The position of a body in motion changes with time...False
E)The acceleration of a body with zero speed is zero...False
F)Motion and acceleration are not the same quantity...True

I'm sorry to be a stickler here, but which teacher would set such dumb, ambiguous questions for students ?


My answers would be different for A and E :

A)The speed of an accelerated body changes with time... Not necessarily, but unable to determine if true or false from just this.

E)The acceleration of a body with zero speed is zero...Again, not necessarily, but unable to determine if true or false from just this

If the questions had included the critical word necessarily then they would be OK, but as they stand, I consider them inadequate and misleading.

 

[jdavel]

If the questions had included the critical word necessarily then they would be OK, but as they stand, I consider them inadequate and misleading.

When an answer of "true" or "false" is asked for, true means "always true" and "false" means "not always true".

 

[Pengwuino]

When an answer of "true" or "false" is asked for, true means "always true" and "false" means "not always true".

yah, "is" always denotes "true = always true"

 

[Curious3141]

When an answer of "true" or "false" is asked for, true means "always true" and "false" means "not always true".

Hmmph, where did such an idiotic convention come from, and are the students taught to assume this by default ? No wonder most of them do so poorly at formal logic, they're not even taught the correct meanings of false and true !

It's all well and good to have this sort of convention for binary dichotomous choices. But I've seen more "complex" truth type questions, where there are choices for T, F, Insufficient info. If faced with a three pronged choice like that, I'd go for the third one, but it can be confusing if students have been taught all along that T = always, necessarily true and F = not always true, but not necessarily false either.

 

[jdavel]

Curious,

Is the statement "Odd numbers are prime numbers" true, false, or is there "insufficient info" to say one way or the other?

I see no difference (logically) between that statement and the statement "The acceleration of a body with zero speed is zero."

 

[Curious3141]

Curious,

Is the statement "Odd numbers are prime numbers" true, false, or is there "insufficient info" to say one way or the other?

I would consider the above statement to be ambiguous. I understand that the intended implication is that a general odd number is necessarily a prime (which of course is FALSE), but it is still possible for confusion with the alternative implication that certain specific odds can be prime (which is TRUE). I would be comfortable with this sort of statement in a conversation, where clarification can always be sought, but not in a textbook, and certainly not in a graded test.

Maybe it's just me, but I expect strict logical clarity in my test questions.