The sum of four natural numbers is 2235.  If delete units digit of the first number, we get the second number. If delete units digit of the second number, we get the third number. If delete units digit of the third number, we get the four number .Find the first number.

$\frac{2}{3}$ of the sum of two numbers subtracts the difference of those two is equal to 32. If $\frac{1}{2}$ of the difference of the two numbers multiplies by 6 then the result is equal to the sum of two numbers? Find the two numbers.

A natural number with 5 digits is given. Knowing that if the number is multiplied by 4, we have a new number which can be written using the digits of first number but in the opposite order ? Find the original number.

Four numbers are given which are different than each other and 0. Find the sum of all numbers which can be written by the given four numbers, knowing that the sum of the greatest and smallest number is equal to 9889.

Natural numbers from 1 to 100 are split into 2 groups: odd numbers and even numbers. What is the difference between the sum of digits of odd number and even numbers?

How many “0” digits appear in the sequence from 0 to 99999 ?

Four consecutive natural numbers are written as thousands, hundreds, tens and units of a 4-digit number. Write the digits of that number in reverse order and we have a new 4-digit number which is greater that the original number by how many units?  

Find a natural number. Knowing that if adding that number to the sum of its digits , we have a result of 1159.

A 2-digit number is divided by the sum of its digits, giving a quotient of 4 and remainder of 3. If changing the position of the digits, the difference between the new number and the sum of its digits times 6 is equal to 5 units. Find the original number.

A natural number is written with the digits of 12345678………19981999. Find the sum of its digits.

A man is asked: “ How long have you joined the army?”. He replies: “My military years is $\frac{1}{27}$ of my age and $\frac{1}{7}$ of the age of my son. My age is closer to number 90 than number 100. How long has he joined the army?

The weigh of four cups and a teapot is equal to the weigh of 17 pencil leads. The weigh of a teapot is equal to the weigh of 7 pencil leads. The weigh of a teapot is equal to how many pencil leads?

A fisherman is asked how heavy the fish he caught is. He replies: “The tail weighs 150g, the mass of its head is equal to the sum of tail’s weight and $\frac{1}{2}$  the weight of its body, while the fish’s body weight is equal the weight of head and tail. What is the weight of the whole fish? 

A farmer brings two egg baskets to the market, each basket has 30 eggs. In the smaller basket, she plans to sell 3 eggs for 1 dollar . In the biger basket, she will sell 2 eggs for 1 dollar. However, at the market, she changes her mind. The farmer mixes up eggs in both baskets and sells 5 eggs for 2 dollars. How much does she lose?

A girl brings two egg baskets to the market. A boy accidentally pushes her so she drops the two baskets. All eggs are broken. He apologizes to her and askes how many eggs are there altogether. She says: “I didn’t count but when I put 2 eggs each time in each basket, or 3 eggs each time, or 4 eggs each time, 5 eggs each time or 6 eggs each time, there will always one spare egg. But when I put 7 eggs each time in each basket,  there is no spare egg left”. How many eggs are there?