Math practice for 13 year olds - page 353 of 423

Number of problems found: 8457

Distilled water
Seawater contains 5% salt. How much distilled water should be poured into 40 kg of seawater so that the salt content is 2%? How many kilograms of 2% of seawater do we get?
Difference 3101
The difference between the two numbers is 4/3. If you know that the first number is 50% larger than the second number, specify both numbers.
Water temperatures
To 25 liters of water at 50 °C, we add 15 liters of water at a different temperature. How many °C should the water be colder than 50 °C so that 40 liters of the water obtained has a temperature of 42.5 °C?
Concentration 3098
Calculate the concentration of the solution prepared from 6 kg of 95% sulfuric acid solution and 24 kilograms of 10% sulfuric acid solution.
Concentration 3097
How many liters of 60% and 80% formic acid do we have to mix to get 80 liters of this acid with a concentration of 65%?
Candy
The price for 1kg of more expensive candy is 125 CZK. The price for 1kg of cheaper candy is 100 CZK. We make two different blends of candy. And now. The second blend contains 2 kilograms of more expensive candy and several kg of cheaper candy. The price p
Kilograms 3094
1.5 kg of a 20% NaCl solution should be diluted to a 10% solution with water. How much water will we need, and how many kilograms of diluted solution will we get?
Solution 3092
How many liters of 80% alcohol need to be mixed with 4 liters of 40% alcohol to get 70% alcohol? How many liters of 70% solution do we get?
Numbers 3090
The sum of the two numbers is 52.5. The first number makes up 75% of the second number. Specify both numbers.
Solution
What amount of 80% solution and water is needed to mix to obtain two liters of 60% solution of this mixture?
Circumference 3088
In the parallelogram ABCD, the side AB is three times longer than the side BC. The circumference of the parallelogram is 20 cm. Find the lengths of the sides of the parallelogram.
Savings 3087
Milan has 84 euros. He gave his brother 20% of his savings and his sister 25%. Find how much money each has.
Two-digit 3085
How many two-digit numbers can you create from the digits 7,0,1 and 5 if the numerals can be repeated?
Mr. John
Mr. John wants to buy winter apples Spartan. There are two ways to buy: 1) buy apples at the marketplace, where 1 kg costs 15 CZK. 2) Bring the car to the agricultural farm, where the apples are sold for 9 CZK per kilogram. However, he must pay CZK 150 fo
Contestants
In the competition, it was possible to get 0-5 points. Five of the 15 best contestants have earned 5 points or 4 points (which have won 10 contestants). The number of contestants who scored 3 points was the same as those who did not get any points. Calcul
Tiles path
A rectangular park measures 24m X 18m. A path 2.4m wide is constructed all around it. Find the cost of paving the path with cement tiles of size 60cm X 40cm at the rate of $5.60 per tile.
Digging
A pit is dug in the shape of a cuboid with dimensions 10mX8mX3m. The earth taken out is spread evenly on a rectangular plot of land with dimensions of 40m X 30m. What is the increase in the level of the plot?
Fog
The car started in fog at a speed of 30 km/h. After a 12-minute drive, the fog dissipated, and the driver drove the next 12-minute distance, 17 km. The driving conditions deteriorated during the last 17 km, and the driver drove at 51 km/h. a) Calculate th
Probability 3065
Natural numbers 4,5,7,11,12 are given. Calculate the probability of the event that the sum of three randomly selected numbers is less than 22.
Class 9A
On the final certificate, one-quarter of the class 9A marked “C” in mathematics, the seventh mark “C” from the Czech language, and two students failed in chemistry. How many students attend class 9A?

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