# Statistics + reason - math problems

#### Number of problems found: 59

• Chi square
A manufacturer of phone batteries claims that his batteries' lives are approximately normally distributed with a standard deviation equal to 0.9 years. If a random sample of 10 of these batteries has a standard deviation of 1.2 years. Do you think that th
• Energy saving
They were released three different, independent inventions saving 20%, 24% and 15% energy. Some considered that while the use of these inventions, the total savings will be 20% + 24% + 15% = 59%. Is this true? How much will percent of energy save all thre
• Target
Peter, Martin and Jirka were fire in a special target, which had only three fields with values of 12, 18 and 30 points. All boys were firing with the same number of arrows and all the arrows hit the target, and the results of every two boys differed in on
• Gas prices 2021
According to the SPP price list in 2021, the price of natural gas together with its supply is as follows: D1 - we cook. Fix 3.34 euros/month and 0.0479 euros/kWh (1 cubic meter of gas is approximately 10.555 kWh. It is called combustion heat and changes o
• Marks at school
There are 30 students in the class. Five students in the class had a mark three triple at the end of the math certificate, and the other students had a mark of one or two. The average mark in all students' mathematics in the class at the end of the year w
• In the
In the 6th class, the average half-year mark in physics was 1.7. At the end of the year, Maťo improved his mark from 2 to 1, Ivanka from 3 to 2, and Elenka from 4 to 2. Pavlík worsened his mark from 3 to 4. The average mark of the whole class thus improve
• Big family
A certain number of people met at the family celebration - their average age was three times the number present. Then came my grandfather, who was 75 years old and the average age was again three times the number present. How many people are celebrating r
• Average age
The company of five people has an average age of 46 years. The average age of the first four is 43 years. How many years has the fifth member of this company?
• Team
The football team has 11 players. Their average age is 20 years. During the match due to injury, one player withdraws and the average age of the team is 18. How old was injured player?
• There
There are 24 students in the class. On Friday, the math class is divided into 2 groups of 12 students. The table shows the results of pupil assessment in 2 groups. Three students in the 1st group have a grade worse than the students in the 2nd group, the
• Nuts
Peter has 49 nuts. Walnuts have 3 more than hazelnuts and hazelnut 2 over almonds. Determine the number of wallnuts, almonds and hazelnuts.
• Young mathematician
One young mathematician was bored again. He found that the average age of people in the room where the seminar equals to its count. Then his 29-year-old brother entered this room. Even then, the average age of all present was the same as the count of peop
• Enterprise and wages
The enterprise operates a total 162 workers and their average salary is M dollars. If the company has hire an additional 18 employees whose average wage would be the S dollars, would reduce the overall average salary in the company of 3.6%. Calculate the
• Beer tapping
When checking compliance with the beer tapping, it was found that 60% of the offered beers were underfilled. The others were fine. Thus, instead of 0.5 l, the volume was 4.4 dcl on average. What was the volume of one average underfilled beer?
• Troops
There are two leaders in the tourist group, with an average age of 30 years and several children with an average age of 10 years. The total age of the group is 12 years. How many children are in the group?
• Average weight
Mom bought 6 apples with an average weight of 130 g - If she took 1 apple out of the bag, the average weight of the remaining apples changed to 140 g. What was the weight of the removed apple?
• Grandfather
The grandfather is three years older than a grandmother. The average age of the grandmother, the grandfather, and their seven grandchildren is 28 years. The grandchildren have a total of 105 years. Calculate how old grandfather is.
• Before yesterday
He merchant adds a sale sign in his shop window to the showed pair of shoes in the morning: "Today by p% cheaper than yesterday. " After a while, however, he decided that the sign saying: "Today 62.5% cheaper than the day before yesterday". Determine the
• Apple collecting
Luke, Peter and Tibor compared how many kilograms of apples they had collected. They found that the arithmetic mean of what Luke and Peter collected was 10 kg larger than Tibor's contribution, and the arithmetic mean of what Luke and Tibor collected was 3
• Average monthly salary
A total of 10 teachers work at one small school in Moravia. The monthly salary of each is 21,500 CZK or 21,800 CZK or 22,500 CZK according to their education and age. The average monthly salary for this school's teacher is 21 850 CZK. How many teachers of

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