Fill the 5-by-5 grid with the digits 1, 2, 3, 4, 5 so that each digit occurs exactly once in every row and every column. What digit belongs in the cell marked X?
Hùng rolls a four-sided die numbered 1 to 4 and a six-sided die numbered 1 to 6. Each time, he subtracts the smaller result from the larger, recording 0 if they are equal. How many different results can he obtain?
Su made the chart to show the animals seen at the zoo. How many more crocodiles than lions did Su see? From left to right, the categories are crocodiles, monkeys, zebras and lions.
Complete the grid so that each of the numbers 1, 2, 3 and 4 appears exactly once in every row and every column. What number goes in the bottom-right cell marked with a question mark?
A beaver takes 2 minutes to saw a log into 2 pieces. At the same rate, how many minutes does it take to saw the log into 7 pieces? Each cut is through one piece at a time.
All outside faces of the rectangular block are painted red. It is then cut into the 18 equal small cubes shown. How many small cubes have exactly two painted faces?
There are 13 flowers. Five are chrysanthemums and the rest are roses. Six flowers are white and the rest are yellow. What is the greatest possible number of yellow roses?
No two students have the same rank. An is 8th from the top, and Bình is 5th from the bottom. Exactly 2 other students are ranked between them. What is the smallest possible number of students in the class?
There are 18 birds on two branches. First, 3 birds fly from the first branch to the second. Then 5 birds fly from the second branch to the first. The two branches now have equal numbers of birds. How many birds were initially on the first branch?
Today is Sunday. What day of the week will it be 18 days later? Enter the given code: Monday 0002, Tuesday 0003, Wednesday 0004, Thursday 0005, Friday 0006, Saturday 0007, Sunday 0008.
Đào and Hằng start with the same number of candies. Each day Đào eats 3 candies and Hằng eats 2. After some days, Đào has 4 candies left and Hằng has 9. How many candies did each girl have at first?
Initially, tank A contains three times as much water as tank B. After 6 litres are added to A and 7 litres to B, A contains twice as much water as B. How many litres were initially in A?