The variance of a set of 20 observations is 16 . If 7 is added to each observation, and then $\mathbf{5}$ is subtracted from each resulting observation, what will be the new standard deviation?
4
9
18
2
$$ \text { If }(\vec{a}+\vec{b}) \perp \vec{b} \text { and }(\vec{a}+2 \vec{b}) \perp \vec{a} \text {, then } $$
$$ 2|\vec{a}|=|\vec{b}| $$
$$ |\vec{a}|=2|\vec{b}| $$
$$ |\vec{a}|=|\vec{b}| $$
$$ |\vec{a}|=\sqrt{2}|\vec{b}| $$
Let the population of a species of birds surviving at a time ' $\boldsymbol{t}$ ' be governed by the differential equation $\frac{d p}{d t}-p=-100$. If $p(0)=50$, then $p\left(-\log _e 2\right)$ is equal to
100
90
75
40
A coffee roaster has $\mathbf{1 2}$ rare coffee beans with intensity scores ranked from $\mathbf{1}$ (mildest) to $\mathbf{1 2}$ (strongest).
You choose 7 beans at random and line them up from mildest to strongest:
$$ C_1< C_2< C_3< C_4< C_5< C_6< C_7 $$
What is the probability that the third bean $\left(C_3\right)$ has an intensity score of exactly 4 ?
$\frac{1}{4}$
$\frac{21}{44}$
$\frac{5}{18}$
$\frac{35}{132}$
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