Harmonic mean - practice for 14 year olds
Number of problems found: 98
- Together 83245
Jarka and Jana decided to decorate their common room. If Jarka painted it alone, it would take her 4 hours, and Jane 3 hours. How long would they paint the room if they painted together? - Together 82965
An older digger would dig a ditch by himself in 6 hours. A younger digger can handle the same trench in 3 hours. How long would it take them to dig if they worked together? - Simultaneously 82806
An empty tank is filled with inflow in 30 minutes. A full tank is emptied in 75 minutes with an open drain. How long does it take for an empty tank to fill up if both the inlet and outlet are open simultaneously? - Excavators 82208
Two excavators dig a pit in 12 days. How much shorter will this job take if 8 excavators dig the hole? In 3 or 9 days? - Throughout 82075
In the metro, trains run in one direction at the same speed and the same intervals. Yesterday, there were 24 trains throughout the day. More trains will run today, as the time interval between trains will be shorter by 20%. How many more trains will there - Basement 81681
After the flood, the Nováks would pump water out of the basement with one pump in 120 minutes, the second in 300 minutes, and the third in 600 minutes. How many minutes will it take them to pump the water out of the basement if they use all the pumps at o - Apartment 81654
A woman cleans an apartment in 8 hours and a man in 10 hours. How many hours will they clean together? - Together 81046
Two painters are painting the factory fence together. If everyone worked alone, the first would finish the job in 16 days, the second in 20 days. When will they finish the work together? - Construction 71794
Two different trucks together would bring the construction material in 6 hours. However, after 4 hours, the first car was transferred to another job, and the second one was driven for another 6 hours. How many hours would it take for the first car to deli - Apartment 71114
A father and son paint the apartment together in 6 hours. My father would paint the apartment in 9 hours. In how many hours would the son paint the apartment himself? - Restaurant 65394
The restaurant was fully booked at lunchtime. While only three waiters staffed the restaurant, guests waited an average of 45 minutes for the lunch menu. On average, how many minutes will the guests wait if the three waiters are joined by two more waiters - Together 65074
Jana washes 20 windows alone in 4 hours. Petra would be able to do it in 6 hours. How long will it take to work together? - Pentagon
The signboard has the shape of a pentagon ABCDE, in which line BC is perpendicular to line AB, and EA is perpendicular to line AB. Point P is the heel of the vertical starting from point D on line AB. | AP | = | PB |, | BC | = | EA | = 6dm, | PD | = 8.4dm - Blueberries 48771
Mirka picks up a bucket of blueberries in two hours. Lojzo fills one-third of the bucket every hour. How long would it take to fill one bucket together to the brim? - Assemblers 47483
Two assemblers with the same daily output were to complete the assembly in 12 days. After 4 days, one of them got sick, and the other finished the assembly in another 16 days. How long would it take everyone to do the assembly by themselves? - Average speed
The car drove on one section of the highway for half an hour at a speed of 80 km/h. Then he reduced his speed to 60km/h. It went three-quarters of an hour at a speed of 60 km/h. What was the average speed of the car? - Treatment 46571
They have 3 sprayers for the chemical treatment of the vines. The first would spray the vineyard in 12 hours, the second in 15 hours, and the third in 10 hours. How long would it take to spray the vineyard with all the sprayers combined? - Two cables
On a flat plain, two columns are erected vertically upwards. One is 7 m high, and the other 4 m. Cables are stretched between the top of one column and the foot of the other column. At what height will the cables cross? Assume that the cables do not sag. - Truncated 43851
The pit has the shape of a regular truncated 4-sided pyramid, the base edges of which are 14m, 10m, and the depth is 6m. Calculate how many m³ of soil were removed when we dug this pit. - Average speed
The car drove from city A to city B at 40 km/h and back to city A at a speed of 80 km/h. What was the average speed of the car?
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