150 students is 60 kg the mean of body is 70 kg withstandard deviation of 10 kg and mean weight of girls is 55 kg with standard deviation of 15kg.calculate the number of boys and the combined standard deviation. Also find whether the coefficient of deviation is hired for girls or boys.

Please proof read

does body mean boys?
what is 60 kg ?
who got hired for what?

http://davidmlane.com/hyperstat/z_table.html

1. The probability that a freshman entering Bahir Dar University will survive first semester is

0.89. Assuming this pattern remain unchanged over the subsequent years, what is the probability
that among 100 randomly selected freshmen students in first semester,
a) None will survive? b) Exactly 97 will survive c) At least three will survive�

Answer of questions

To solve this problem, we can use the concept of weighted averages and standard deviations.

Let's start by finding the number of boys.

1. Let's assume the number of boys is "B" and the number of girls is "G."
2. According to the given information, there are 150 students in total. So we can write the equation: B + G = 150.

Next, let's calculate the combined standard deviation.

1. The formula to calculate the combined standard deviation is given by:
Combined Standard Deviation = √((n1-1)s1^2 + (n2-1)s2^2 + ... + (nk-1)sk^2) / (n1 + n2 + ... + nk)
where n1, n2, ..., nk are the sample sizes, and s1, s2, ..., sk are the respective standard deviations.

2. In our case, we have two groups - boys and girls. The formula becomes:
Combined Standard Deviation = √(((B-1)(10)^2) + ((G-1)(15)^2)) / (B + G)

Now we have two equations:
B + G = 150 (Equation 1)
Combined Standard Deviation = √(((B-1)(10)^2) + ((G-1)(15)^2)) / (B + G) (Equation 2)

To find the values of B and G, we will use these equations simultaneously.

Let's solve the equations:

1. Simplify Equation 2:
Combined Standard Deviation * (B + G) = √(((B-1)(10)^2) + ((G-1)(15)^2))

2. Square both sides to eliminate the square root:
(Combined Standard Deviation)^2 * (B + G)^2 = ((B-1)(10)^2) + ((G-1)(15)^2)

3. Substitute the value of B from Equation 1 into the equation above:
(Combined Standard Deviation)^2 * (150 - G)^2 = ((150 - G - 1)(10)^2) + ((G-1)(15)^2)

4. Expand and simplify:
(Combined Standard Deviation)^2 * (150 - G)^2 = (14400 - 200*G + G^2 + 225*G - 225 + 100*G - 10*G^2 + 225)

5. Further simplify and rearrange:
(Combined Standard Deviation)^2 * (150 - G)^2 = -9*G^2 + 125*G + 14250

6. Rearrange the equation:
(Combined Standard Deviation)^2 * (150 - G)^2 -(-9*G^2 + 125*G + 14250) = 0

To solve this quadratic equation and find the value of G, you can use the quadratic formula:

G = (-b ± √(b^2 - 4ac)) / 2a

Here, a = -9, b = 125, and c = 14250.

Substituting these values into the equation will give you the two possible values for G. From there, you can find the value of B using Equation 1.

Once you have the values of B and G, you can calculate the coefficient of deviation for both boys and girls by dividing their respective standard deviations by their mean weights. The group with the higher coefficient of deviation will indicate a higher variation in weights.

9000=70x+8250-55x

Boys 50
Girls 100