Harmonic mean + reason - math problems

Number of problems found: 18

  • Aircraft angines
    The two engines of the aircraft are enough to supply the fuel for five hours of operation. However, one of the engines has a malfunction 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
  • Water current
    John swims upstream. After a while, he passes the bottle, from that moment he floats for 20 minutes in the same direction. He then turns around and swims back, and from the first meeting with the bottle, he sails 2 kilometers before he reaches the bottle.
  • Uphill and downhill
    The cyclist moves uphill at a constant speed of v1 = 10 km/h. When he reaches the top of the hill, he turns and passes the same track downhill at a speed of v2 = 40 km/h. What is the average speed of a cyclist?
  • Four pavers
    Four pavers would pave the square in 18 days. How many pavers do you need to add to done work in 12 days?
  • Two cities
    The car goes from city A to city B at an average speed of 70 km/h, back at an average speed of 50 km/h. If it goes to B and back at an average speed of 60 km/h, the whole ride will take 8 minutes less. What is the distance between cities A and B?
  • Express train
    International express train drove from Kosice to Teplice. In the first 279 km, the track was repaired, and therefore it was moving at a speed of 10km/h less than it was scheduled to drive. The rest of the 465 km trip has increased the speed by 8 km/h than
  • Harvesters
    The first harvester will harvest the grain from the field in 20 hours, 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 and this takes 2 hours? The fir
  • ICE train
    German runways test a new ICE train between Munich and Berlin. The train runs to Berlin at a slow speed of 100 km/h. Back from Berlin goes faster. How quickly did the train have to go on a return trip so that the total average train speed for both journey
  • Mow the lawn
    Dano would mow the lawn in 12 hours and Milada in 16 hours. How long will take the lawn mow together?
  • Oil tank and pipes
    The underground oil tank can be filled by two oil pipelines. The first is filled in 72 hours and the second in 48 hours. How many hours from the moment when first pipeline began to fill the oil is it necessary to start filling it with the second to fill i
  • Timber log
    The ship goes from point x to y. Downstream it takes 4 hours, upstream 6 hours. How long does it take from a point x to y a log?
  • Three drivers
    Three driversdriving the same direction found that they have same amounth of gasoline. The first is enough to go 6 km, 4 km second and third 3km. Gasoline they divided so all three just drove to the nearest petrol station. How many km away was a petrol st
  • Forth and back
    Car drive from point A to point B at speed 78 km/h and back at 82 km/h. If went there and back at speed 81 km/h journey would take five minutes less. What is the distance between points A and B?
  • Drinking water
    A man drinks a keg of water in 40 days, and a woman drinks in 62 days. How many days do they consume a keg together?
  • Pool
    If water flows into the pool by two inlets, fill the whole for 19 hours. The first inlet filled pool 5 hour longer than the second. How long pool take to fill with two inlets separately?
  • Cyclist
    The cyclist goes uphill 10 km for 50 minutes and downhill minutes for 29 minutes, both applied to the pedals the same force. How long he pass 10 km by plane?
  • 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
  • Tractors
    Fields go plow two tractors with various performances. The first tractor plows the whole field in 11 hours, the second tractor plows the whole field 19 hours longer. How long take plow the whole field with two tractors?

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