3 is added to a certain number and this sum is multiplied by 2 , the number so obtained is equal to the difference of the first number and 9. What is that number?

What is atomic number and mass number?

When a number is multiplied by 3 and then added to 4, 31 is obtained Express this as one equation.

Amina thinks of a number and subtracts frac(5)(2) from it. She multiplies the result by 8. The result now obtained is 3 times the same number she thought of. What is the number?

Find the sum of first n even natural numbers.

A positive number is 5 times another number. If 21 is added to both the numbers, then one of the new numbers becomes twice the other new number. What are the numbers?

The first term of an AP is 5,the last term is 45 and the sum is 400.Find the number of terms and the common difference.

Form the pair of linear equations in the following problems,and find their solutions(if they exist) by the elimination method:(iii) The sum of the digits of a two-digit number is 9.Also nine times this number is twice the number obtained by reversing the order of the digits.Find the number.

The sum of a number and its positive square root is 6/25 .Find the numbers.

What is the sum of the cubes of first n natural numbers?

A rational number is such that when you multiply it by frac(5)(2) and frac(2)(3) add to the product, you get -frac(7)(12) . What is the number?