- A10
- B15
- C20
- D12
Step-by-Step Solution
Let the second group have numbers. Then , so , giving and . (Check: the combined mean 20 lies closer to 18, so the second group must be the smaller one.)
Answer: B) 15
The mean of a group of 30 numbers is 18 and the mean of a second group of numbers is 24. When the two groups are put together the mean of all the numbers is 20. How many numbers are in the second group?
Competition practiceData & Probability
Master this topic in 30 minutes a day.
Don't just memorise the answer — build a daily practice habit.
Practice 5 Similar Questions Free →All Data & Probability practice questions
More Data & Probability practice
In a game a fair die is rolled once. The player receives ₹30 if a 6 appears and pays ₹6…The variance of a data set is 25. If 6 is added to every observation of the set, what is…Bag A contains 3 red and 5 white balls; Bag B contains 4 red and 4 white balls. A bag is…Number of patients treated in four weeks — Clinic A: Week1 45, Week2 60, Week3 55, Week4…For the grouped data 0–10: 5, 10–20: 15, 20–30: 20, 30–40: 8, 40–50: 2 (class interval:…