Answer:
Step-by-step explanation:
given that certain tubes manufactured by a company have a mean lifetime of 800 hours and a standard deviation of 60 hours.
Sample size n =16
Std error of sample mean =
x bar follows N(800, 15)
the probability that a random sample of 16 tubes taken from the group will have a mean lifetime
(a) between 790 and 810 hours,
=
(b) less than 785 hours
, (c) more than 820 hours,
(d) between 770 and 830 hours
=
Answer:
The number of boys are 18 and the number of girls are 30.
Step-by-step explanation:
The ratio of number of girls to the boys = 3 : 5
Let the number of girls is g and boys is b initially.
b : g = 3 : 5
5 b = 3 g ..... (1)
Now, girls are 6 + g and boys are b - 9
So, the ratio is
(b - 9) : (6 + g) = 1 : 4
4 b - 36 = 6 + g
4 b - g = 42 .... (2)
From ( 1 ) and ( 2 )
And , g = 5 x 18/3 = 30
So, the number of boys are 18 and the number of girls are 30.