To round up or to round down?

[crayolé]

When doing exponential modelling, you always get the questions that ask you
a) How many rabbits will there be after 10 years?
or
b) How many months will it take to take this element to decay and when will this occur if the initial date was January 1?

I've recently come across a lot of confusion as whether to round up or down. The textbook answers do both which confuses the heck out of me but my teacher says to always round down?

Say for question a my answer was 78.9 rabbits.
You cant have .9 of a rabbit so would you round down in this case? but in theory we know that the equation is only an approximate and there could very well be 79 rabbits.

For question b say my answer was 7.8 months
Do we say 7 months or 8 months?
Would the answer be August 24th?

[superflya]

a) round down. u cant have 0.9 of a rabbit.

b) round up to 8.

[vexx]

^ with rounding you always round up to the closest whole number i though, so 78.9 is pretty close to 79, hence rounded up to ~79.

[stonecold]

a) round down. u cant have 0.9 of a rabbit.

b) round up to 8.

[Yitzi_K]

^ with rounding you always round up to the closest whole number i though, so 78.9 is pretty close to 79, hence rounded up to ~79.

But you don't have 79 rabbits, and you do have 78. So how can you say 79?

[stonecold]

i actually believe 7.8 months is perfectly acceptable, because a month is continuous data, and unless the question says to specify to the nearest month, how can you be wrong...

[vexx]

^ with rounding you always round up to the closest whole number i though, so 78.9 is pretty close to 79, hence rounded up to ~79.

But you don't have 79 rabbits, and you do have 78. So how can you say 79?

78.9 is close enough to round to 79 isn't it?
.________.
i'd fail that question then if i had it. haa

[m@tty]

Haha, you have 79 rabbits but one is missing legs...

[superflya]

^^ i think one whole leg is a lil too much

[shokstar]

You always round up. with B, if you round down to 7, it wont reach that point that it asks you about. If you round up, at least you have reached the point it asks you about.

[vexx]

Haha, you have 79 rabbits but one is missing legs...

haha exactly! perhaps they'll be open to justification?

[Nomvalt]

would it be appropriate to keep it in exact form? i was told that we didn't have to worry about rouding in methods as we must keep everything in exact form.

[Yitzi_K]

would it be appropriate to keep it in exact form? i was told that we didn't have to worry about rouding in methods as we must keep everything in exact form.

For numbers that would be true, but we're talking rabbits... you can't have a fractional or decimal amount of rabbits.

[TrueTears]

unless this was expected values, whereas you must have it as exact no matter what...

[|ll|lll|]

would it be appropriate to keep it in exact form? i was told that we didn't have to worry about rouding in methods as we must keep everything in exact form.

Speaking of which, do we need to rationalise surds in our answers? my teacher says no... (sorry off-topic)