Statistics: set 3
10 questions. Click an option: a correct answer turns green, a wrong one red, and an explanation appears.
An internet provider has 1 200 customers: 800 in the city and 400 in rural areas. For a survey, a sample of 150 people is drawn with proportional allocation to the groups. How many people are selected from the city customers?
The base indices of a canteen's revenue relative to 2024: 110% in 2025 and 132% in 2026. What is the chain growth rate of 2026 relative to 2025?
Waiting times in the queue for six customers at a bank branch (minutes): 12, 7, 15, 9, 20, 10. What is the median of this series?
Daily deliveries of four couriers: 3, 5, 7, 9 (mean 6, variance 5 when calculated by dividing by n). The next day each courier delivered exactly 5 more: 8, 10, 12, 14. How do the mean and the variance change?
An ice cream workshop calculated the linear correlation coefficient from 12 weeks of price and sales volume data: r = −0.85. What is the correct interpretation of this result?
Grouping of a logistics firm's drivers by length of service: 0–10 years – 4 people, 10–20 years – 10 people, 20–30 years – 6 people. Using the interval midpoints, what is the average length of service?
The average annual population of a hypothetical district is 250 000 people, and 5 000 children were born during the year. What is the crude birth rate (per 1 000 population, in per mille)?
Annual sales of the "Yashil vodiy" plant nursery (mln soum): 2023 – 40, 2024 – 46, 2025 – 49, 2026 – 58. What is the average annual absolute increase for this time series?
The "Qo'qon mexanika" plant employs 240 workers and 30 engineers. Using the relative coordination indicator, how many engineers are there per 100 workers?
Flour stock in a bakery warehouse at the start of each month: 1 January 40 t, 1 February 44 t, 1 March 50 t, 1 April 46 t. What is the average stock for Q1 for a point-in-time series with equal intervals (chronological average)?