Percentages - 8th grade (13y) - math problems

In the classroom
There are 30 boys and a few girls in the class. In the six months, 28 boys and all girls benefited, which was 95% of all pupils. How many pupils are there in the classroom?
Corona again
If the population on long island is 7.75 million and the coronavirus has affected 22,178. What percent of the population is affected. (looking for 1 in? If possible)
Triangular prism
The base of the perpendicular triangular prism is a rectangular triangle with a hypotenuse of 10 cm and one leg of 8 cm. The prism height is 75% of the perimeter of the base. Calculate the volume and surface of the prism.
The surface area
How much percent will the surface area of a 4x5x8 cm block increase if the length of the shortest edge is increased by 2 cm?
What percent
What percent of 51 3/5 is 47 2/5?
Reward
Janko and Peter divided the reward from the brigade so that Peter got 5/8 of the reward. What percentage of Janko's reward got?
Alcohol mixing
How much 64% of the alcohol must be poured into 6 liters of 85% alcohol to produce 79% alcohol?
Altitude difference
What a climb in per mille of the hill long 4 km and the altitude difference is 6 meters?
Nitrogen
One bag of urea containing 46 percent nitrogen weighs 25 kg. How many bags have to be purchased for fertilizing a field of 41003 square meters if the nitrogen dose is 50.0 kg per hectare?
3/8 off
A shirt cost 38.95 How much will you pay for the shirt if it has a discount tag for 3/8 off? Round to the nearest cent
Two accounts
Two accounts in the bank, one per year interest 2%, the second 3%. Total interest income 1900 USD. If interest rates were reversed, the yield would be USD 200 higher. What are the amounts on each account?
The fastest
The fastest boat can reach speeds more than 710% as fast as the Queen Mary 2. How would you express this number as a fraction and as a decimal?
Two accounts
A banker divided $5000 between 2 accounts, one paying 10% annual interest and the second paying 8% annual interest. Express the amount invested in the 10% account in the terms of the amount invested in the 8% account.
Unknown number
15% of the unknown number is 18 less than 21% of the same number. What is the unknown number?
Mary
Mary is 12 years old, which is 40% of the age of her mother. How many percent of her mother's age will Mary have after the next 12 years?
Auto-tuning
During auto-tuning, the TV searched for 25 channels, four of which were music. The channels are stored in the TV's memory in random order. Express the percentage of the event that the music channel will be saved first.
Pouring alcohol
100 liters of alcohol has 70% How many liters of water need to be added to have 60% alcohol?
Cake ingredients
The yeast cake contains milk, yeast, sugar, and flour in a ratio of 20: 4: 1: 15. What percentage of flour is in yeast?
Bdf tablet
Detective Harry Thomson has come across a surprising mystery. As part of the weekend's action, the tablet he looked for dropped by 30%. He also recommended this bargain to his friend. However, it came to the shop on Monday, and the tablet was 30% more expe
The bar chart
The bar chart shows the results of the math test. How many% of pupils achieved approximately better results than the average of the class? Diagram: 1-10 pupils, 2-4 pupils, 3-6 pupils, 4-2 pupils, 5-4 pupils. (lowest result are better)