Harmonic mean - practice for 13 year olds - page 2 of 6
Number of problems found: 104
- 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? - 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? - The leaves
Karel raked the leaves in the garden alone in 24 minutes, and his younger brother took 30 minutes. How long would they dig a garden if Karel digs alone for 6 minutes and his brother comes to his aid?
- Together 28411
Worker A will dig a trench in 12 days. Worker B will dig a trench in 18 days. How many days will it take them together? - Cleaning 27663
During the pool cleaning, two drains and one inlet were opened. The first outflow would empty the pool in 6 hours, the second outflow would fill it in 9 hours, and the inflow would fill it in 12 hours. How long will it take to empty if the drains are open - Production 24021
The plant has to complete the order in 40 working days. Production takes place in two workshops. In the first one, there are more workers; therefore, they would complete the order themselves in 70 working days. In the second workshop, they would complete - Simultaneously 17821
The reservoir is filled with the first pump in 30 hours, the second in 24 hours, and the third in 20 hours. How long does it take to fill the reservoir if all pumps are switched on simultaneously? - Aircraft angines
The aircraft's two engines are enough to supply the fuel for five hours of operation. However, one of the engines has malfunctioned and thus consumes one-third more fuel. How long can the plane be in the air before it runs out of fuel? After an hour of ma
- Panel house
The construction company has two groups of workers. Group A has more members than B. Panel house was insulated by group A for ten days. They insulated the same block of flats together in 6 days. How many days would group B block insulate? - Birdhouse 12941
Michal would make a birdhouse in three hours, and Richard would make it in two hours. If they work together, how many hours will it take them to complete it? How much percent more time compared to the time of working together would Michal make the booth b - Mixture of nuts
We should prepare the mixture of nuts from almonds, peanuts, and nuts cashew ratio of 1:2:3 (respectively). The price of almonds is 150 CZK/kg, the price of peanuts is 140 CZK/kg, and the price of cashew nuts is 180 CZK/kg. The price of the mixture is det - Between two bus stops
Wanda lives between two bus stops at three-eighths of their distance. He started the house today and found that he would have arrived at the bus stop if he had run to one or the other. The average bus speed is 60 km/h. What is the average speed of Wanda r - Average speed
The truck drove 1/2 of the way on the highway at 80km/h. The other half of the way, 20km/h. Calculate the average speed
- Reading records
Lucy, Tereza, and Petra decided to compile the compulsory reading records together. It would take 30 days for Lucia alone, 36 for Tereza, and 45 for Petra. How long will it take to make records if they will work together? - Four pavers
Four pavers would pave the square in 18 days. How many pavers do you need to add to the done work in 12 days? - Minutes 8081
I will drain the whole tub in 4 minutes. How long would it take to drain it if I added two more drain holes? - Ten cashiers
Ten cashiers are open at Tesco. Customers wait an average of 15 minutes. How many other cashiers have to open to reduce the waiting time by 4 minutes? - Flowerbed
Ondra digs the bed in 20 minutes. Cuba in 30 minutes. For how long do they dig together?
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