Harmonic mean - practice for 12 year olds
Number of problems found: 40
- Corrects 83017
The new teacher corrects papers for 9 hours, and the older one fixes them in 6 hours. How much will they repair together? - Companies 82884
The K+S company will mow the meadow in ten hours. The Kosačka company mows the meadow in six hours. How many hours would these companies mow one such meadow if they worked together? - Developed 64664
The cyclist in the 1st stage covered 70 km at a speed of 22.1 km/h. In the 2nd stage, he covered 40 km (a total of 110 km), and his average speed increased to 22.9 km/h. What an average speed he developed in the 2nd stage. - 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
- Remaining 8931
The car driver plans to drive to a distance of 30 km in 0.5 hours. For twenty minutes, he follows the column at a speed of 30 km/h. What speed would he have to go in the remaining time? - 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? - Flowerbed
Ondra digs the bed in 20 minutes. Cuba in 30 minutes. For how long do they dig together? - Half-filled 7336
The water tank is filled with the first inflow in one hour and 10 minutes and the second in 60 minutes. How many minutes will the tank be half-filled with both inlets if the second outlet is opened 12 minutes later? - Calculation 7334
In a computer center, one computer would work 12 hours to solve a task, and another, more powerful, would solve the same task for 10.5 hours. If both computers work together, the calculation time would be reduced for a certain period. Calculate how long i
- The factory
The factory z can complete an order in 12 days, factory p in 18 days. How many days does an order completed when the first two days work only the factory z and then both factories? - Harvesters
The first harvester will harvest the grain from the field in 20 hours, and the second, the more powerful in 10 hours. How long will it take to harvest this field by both harvesters if the second harvester has to be set up first, which takes 2 hours? The f - Soldier
An experienced soldier digs a good trench in 30 hours. Two soldiers dug the same trench every 40 hours. How many hours will the ditch dig all three together? - Together 3
If Sally can paint a house in 4 hours, and John can paint the same house in 6 hours, how long will it take for both of them to paint the house together? - Three painters
The three painters have painted bridges. The first would work done in 5 days, the second in 6 days, and the third in 7.5 days. How long will the bridge work if they work together?
- Three pumps
The water tank is emptied with the first pump in 6 hours, with the second pump in 2 hours. In order to be emptied in 1 hour, all three pumps had to be started at once. How long will it take to empty the tank by only the third pump? - In and out
The empty tank is filled in 12 minutes and empty in 16 minutes. How long does it take to fill if we forget to close the drain? The tank has 1000 liters of volume. - Mow the lawn
Dano would mow the lawn in 12 hours and Milada in 16 hours. How long will it take the lawn mow together? - Pond
Workers will empty a pond with two open floodgates in 20 days. A larger floodgate will empty the whole pond in 30 days. For how long would he be emptied with a smaller floodgate? - Oil tank and pipes
Two oil pipelines can fill the underground oil tank. The first is filled in 72 hours, and the second in 48 hours. How many hours from when the first pipeline began to fill the oil is necessary to start filling it with the second to fill in 1 and 1/2 days?
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