According to the world health organization (who) child growth standards, the head circumference for girls who are two-years old has a normal probability distribution witha mean of 47.2cm and a standard deviation of 1.4cm. what is the head circumference of a two-year old girl who marks the start of the 90th percentile? enter a number without units.

Hence, 49.0 cm is the head circumference of a two-year old girl who marks the start of the 90th percentile.    

Step-by-step explanation:

We are given the following information in the question:

Mean, μ = 47.2 cm

Standard Deviation, σ = 1.4 cm

We are given that the distribution of head circumference is a bell shaped distribution that is a normal distribution.

Formula:

We have to find the value of x such that the probability is 0.9

P(X < x)  

Calculation the value from standard normal z table, we have,  

Hence, 49.0 cm is the head circumference of a two-year old girl who marks the start of the 90th percentile.

50 min

step-by-step explanation:

they will be decreasing both their times in half

60 / 2 = 30

40/2 = 20

30 + 20 = 50

x² + 3x + 7 = 0       [ax² + bx + c]

a = 1

b = 3

c = 7

quadratic formula:

    (+/- is this ±)

plug in the numbers into the variables

your answer is a