Examples for 8th grade

Sea water
Mixing 62 kg of sea water with 84 kg rainwater is created water containing 3.1% salt. How many percent sea water contains salt?
Scrap
From 6 products are 3 scrap. What is the probability that the random pick of 2 products have no defective product?
Solution
In 469 dl red solution is 84 dl red color and in 102 dl blue solution is 52 dl blue color. How many dl of red and blue dl color solution must be mixed to get a mixture of 247 dl contain 116 dl of color?
Acids
70% acid was make from same acid of two different concentrations. Amount weaker acid to the stronger acid is in ratio 2:1. What was the concentration of the weaker acid, if stronger had 91% concentration?
Bath
In the bath is 30 liters of hot water. Then added 36 liters of cold water at temperature of 19 °C decreased temperature of water to 41 °C. What was the initial temperature of the hot water?
Trains
On double track line between stations K and M went against each other two trains. The first train passed the distance between stations for 3.5 hours, the second, which had an average speed of 12 km/h more passed for 3.05 hours. Calculate the distance bet
Excavation
Mr. Billy calculated that excavation for a water connection dig for 12 days. His friend would take 10 days. Billy worked 3 days alone. Then his friend came to help and started on the other end. On what day since the beginning of excavation they met?
Sequence
In the arithmetic sequence is a₁=-1, d=4. Which member is equal to the number 203?
Short cut
Imagine that you are going to the friend. That path has a length 120 meters. Then turn doprava and go another 630 meters and you are at a friend's. The question is how much the journey will be shorter if you go direct across the field?
Regular 5-gon
Calculate area of the regular pentagon with side 7 cm.
IS trapezoid
Calculate the length of diagonal u and height v of isosceles trapezoid ABCD, whose bases have lengths a = |AB| = 37 cm, c = |CD| = 29 cm and legs b = d = |BC| = |AD| = 28 cm.
Tape
Video is 153% more expensive than tape recorder. How many percent is tape recorder less expensive than video?
Spherical cap
From the sphere of radius 13 was truncated spherical cap. Its height is 6. What part of the volume is spherical cap from whole sphere?
Elections
The elections attended a total 4818 voters. First day 39 men more than women, the second day 21 women more than men. How many women attended elections?
Pizza
A school survey found that 12 out of 15 students like pizza. If 6 students are chosen at random, what is the probability that all 6 students like pizza?
Coffee
In stock are three kinds of branded coffee prices: I. kind......205 Kc/kg II. kind......274 Kc/kg III. kind.....168 Kc/kg Mixing these three species in the ratio 8:5:6 create a mixture. What will be the price of 100 grams of this mixture?
2x cone
Circular cone height 84 cm was cut plane parallel with base. Volume of these two small cones is the same. Calculate the height of the smaller cone.
Work
First paver pave pavement for 27 hours. Second for 27 hours. Started first paver and after 4 hours, join the second. How long will they finish pavement?
Troops
The route is long 147 km and the first-day first regiment went at an average speed of 12 km/h and journey back 21 km/h. The second day went second regiment the same route at an average speed of 22 km/h there and back. Which regiment will take route long
Camel
Camel owner wants to get out of the city into oasis. He bought 3000 bananas, which wants to sell in oasis. However oasis from the city divided 1,000 kilometers of desert. Camel can carry at one time up to 1000 bananas, and for every kilometer traveled, e

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