A student measured the numbers of stomata per mm of leaf surface. Their counts were: 250, 280, 265, 245, 270, 255, 290.
Calculate the mean number of stomata (to 3 significant
figures).
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When we have  a set of N numbers like:

{x₁, x₂, ..., xₙ}

The mean of the set is:

M = (x₁ + x₂ + ... + xₙ)/N

In this case, we have the set:

{250, 280, 265, 245, 270, 255, 290}

So we have a set of 7 elements.

The mean of this set will be:

M = (250 + 280 + 265 + 245 + 270 + 255 + 290)/7 = 1855/7 = 265

So the mean number of stomata per mm of leaf surface is 265.

the discriminant is 64 + 4*1*12 = 112

this is prime.

step-by-step explanation:

if you are saying purchasing 3 social media ads and one newspaper ad counts as one purchase then there are:

6 purchases

if you are asking how many of each then:

18 social media ads

6 newspaper ads