🎓 Jamia Millia Islamia MCA📅 Year: 2024📚 Mathematics🏷 Probability
1
An urn contains 10 black and 5 white balls. Two balls are drawn from the urn one after the other without replacement.
What is the probability that both drawn balls are black?
The side of an equilateral triangle is increasing at the rate of $2\ \text{cm/s}$.
The rate at which area increases when the side is $10\ \text{cm}$ will be —
For an equilateral triangle, area $A = \dfrac{\sqrt{3}}{4}s^2$
Differentiate with respect to time $t$:
$\dfrac{dA}{dt} = \dfrac{\sqrt{3}}{2}s\dfrac{ds}{dt}$
Given $\dfrac{ds}{dt} = 2$ and $s = 10$,
$\dfrac{dA}{dt} = \dfrac{\sqrt{3}}{2} \times 10 \times 2 = 10\sqrt{3}$
Hence, rate = $10\sqrt{3}$ cm$^2$/s
Dot product $= (5)(3) + (1)(-4) + (-3)(7)$
$= 15 - 4 - 21 = -10$
Wait — recheck:
$15 - 4 - 21 = -10$ (not -15).
Let’s verify carefully — if given answer key shows B (-15), check question once more:
If second vector was $(3i - 4j + 7k)$ indeed,
then $5×3 = 15$, $1×(-4) = -4$, $(-3)×7 = -21$, total = $-10$.
So true answer is $-10$, though the paper marks B ($-15$).
Maybe a misprint.
Let the numbers be $a$ and $b$.
$\dfrac{a + b}{2} = \dfrac{15}{2} \Rightarrow a + b = 15$
and $\sqrt{ab} = 6 \Rightarrow ab = 36$
Now, $a$ and $b$ are roots of $x^2 - 15x + 36 = 0$
$\Rightarrow x = 12, 3$
Hence, the numbers are 12 and 3.