Time + reason - math problems

  1. Birthday paradox
    holland How large must the group of people be so that the probability that two people have a birthday on the same day of the year is greater than 90%?
  2. Large family
    family The average age of all family members (children, mother, father, grandmother, grandfather) is 29 years. The average age of parents is 40 years, grandparents 66 years and all children are 5 years. How many children are there in this family?
  3. The orchard
    jablone 4 temporary workers harvested the orchard in 9 days. How many temporary workers we need for six days?
  4. Troops
    calendar 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?
  5. The tourist
    eq2 The tourist wanted to walk the route 16 km at a specific time. He, therefore, came out at the necessary constant speed. After a 4 km walk, however, he fell unplanned into the lake, where he almost drowned. It took him 20 minutes to get to the shore and re
  6. Fast tourists
    tourist_1 If three tourists pass the route in 5 hours, how long will the same route take six equally fast tourists?
  7. Magnitude of angle
    clocks What magnitude has an obtuse angle enclosed by the hands of clocks at 12:20 hours?
  8. Water current
    river 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.
  9. Harvest time
    clocks2 Grandma and granddaughter Julka reap currants in 15 hours of working together. Julka herself would have currants 10 days after 6 hours of work a day. Find by what percentage the grandma's harvest time was shortened when the granddaughter was involved in
  10. Three lines
    clocks2 At 6 am, three bus lines are departing from the station. The first line has an interval of 24 minutes. The second line has an interval of 15 minutes. The third line runs at regular intervals of more than 1 minute. The third line runs at the same time as t
  11. 45th birthday
    clock-night-schr_1 This year Mrs. Clever celebrated her 45th birthday. Her three children are now 7.11 and 15 years old. In how many years will Mrs. Clever's age be equal to the sum of her children's years?
  12. Family
    age The twins Nina and Ema have five years younger brother Michal. Together have 43 years. How old is Michal?
  13. The tourist
    tourist The tourist traveled 78km in 3 hours. Part of the journey went on foot at 6km/h, the rest of the trip by bus at 30km/h. How long did he walk?
  14. Painters
    time Ten painters paint the school in 20 days. How many days do four painters paint the school at the same pace of work?
  15. Time passing
    clock-night-schr 6 years ago, Marcela's mother was two times older than her and two times younger than her father. When Marcela is 36, she will be twice as young as her father. How old are Marcela, her father, and mother now?
  16. Delayed clock
    clock-night-schr Michael put a new battery into his watch at midnight. However, they are 5 seconds late each minute. How many hours does the watch show in 24 hours?
  17. Assembly parts
    machine Nine machines produce 1,800 parts on nine machines. How many hours will it produce 2 100 parts on seven such machines?
  18. Friction coefficient
    car What is the weight of a car when it moves on a horizontal road at a speed of v = 50 km/h at engine power P = 7 kW? The friction coefficient is 0.07
  19. Uphill and downhill
    cyclist_49 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?
  20. Four pavers
    tiles2_4 Four pavers would pave the square in 18 days. How many pavers do you need to add to done work in 12 days?

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