Câu 9:
The average mass of a group of children is 47kg. If  of the number of children are girls and their average mass is 39kg. Find the average mass of the boys.
Answer: The average mass of the boys is kg
 

Câu 10:
A 6-digit number begins with the digit 8. The number is divisible by 9 and all digits of the number are different. What is the possible smallest value of this number?
Answer: 

1. A 6 digit number begins with the digit 8. The number is divisible by 9 and all digit of the number are different . What is the possible smallest value of this number ?
2. MNPQ is the square that is made up of to identical rectangles and two square of area 9cm2 and 16cm2. The area of the square MNPQ is ?
3. I have two digit in the decimal part.Iam greater than 75 but less than 80 . What least possible number am I ?

The sum of the digits of a ten-digit number is epual to 9.What is the product of the digits of this number?

a) find the next two term in the sequence: 1; 4; 9; 16; 25;....;.....;
Answer: 
b) find the smallest two-digit number whose number is 7 times the sum of its digits? 
Answer:

The sun of the digits of a two-digit number is multiplied by 8.The result is 8 more than the number.Find the two-digit number

Bạn nào làm đc và giải đc mk tick cho  nhiều cái nhé

Find the smallest possible value of the number 368abc so that it is divisible by 3,4 and by 25. 
 

What is the difference between the largest and the smallest possible distinct 4-digit number that you can make from four digits 0, 4, 2 and 3?

choose any three digits from 1 to 9 to form a 3 - digit number and each digits is chosen only once. how many of these have the sum of all digit equal to 13

If we write all of the whole numbers from 10 through 99 and cross out any number in which the first or second digit is divisible by 2 (for example, 41 is crossed out as 4 is divisible by 2 and 36 is crossed out as 6 is divisible by 2), how many numbers are crossed out