Đề tự luyện toán tuổi thơ 2

If a 9-digit number 20213A45B is divisible by 12, find the maximum value of 2A+B.

The area of a rectangle is 432. If sides of the rectangle are integers, find the minimum value of the perimeter of the rectangle.

Choose 3 digits from 0, 1, 2, 3, 4, 5 and 6 to form 3-digit numbers. How many odd numbers lesser than 345 are there? (The repetition of digits is not allowed)

There are 17 blue balls, 16 red balls and 18 yellow balls in a bag. At least how many balls should be picked up to ensure there are 5 balls for each color?

Find the value of  $1\times3+3\times5+5\times7+7\times9+9\times11$