Bảo and Hải have 31 marbles altogether. Bảo gives Hải 5 marbles, but Hải then loses 3 marbles. They now have the same number of marbles. How many marbles did Hải have at first?
Dần gets home at 17:30. He rests for 15 minutes, then bathes for 30 minutes and eats for 40 minutes. He starts studying immediately afterward. At what time does he start?
Hạnh writes consecutive natural numbers on the board. Exactly 8 of them are divisible by 6. What is the greatest possible number of numbers she writes?
Dũng, Hồng and Châu are former classmates. One is a lawyer, one a teacher and one a doctor. Dũng is older than the lawyer. Hồng is not the same age as the teacher. The teacher is younger than Châu. What is Châu’s job? Enter 0001 for lawyer, 0002 for teacher or 0003 for doctor.
The numbers 1 through 9 are placed in the $3\times3$ grid, each exactly once, so that every row, every column and both diagonals have the same sum. Four numbers are already given. Find $X$.
An and Bình start at $S$ and finish at $F$. An follows $S\to A_1\to A_2\to F$; Bình follows $S\to B_1\to B_2\to F$, along the rectangle shown. An walks 10 m farther than Bình. How many meters longer is $A_2F$ than $B_2F$?
A teacher has enough candies to share equally among 4 pupils. When 2 more pupils join, he shares all the candies equally among everyone, and each pupil receives 3 fewer candies than originally planned. How many candies are there?
A test has 15 multiple-choice questions. A correct answer earns 4 points, a wrong answer loses 1 point, and a blank answer earns 0. An answers 8 correctly, 6 wrongly and leaves 1 blank. Khang has the same score and answers 7 correctly. How many questions does Khang leave blank?
On a Grade 3 class outing, all the pupils stand equally spaced around a circle and are numbered clockwise. Minh is number 6 and stands opposite number 14. How many pupils are on the outing?
Giang has a machine with two buttons: one adds 1 to the current number and the other multiplies it by 2. The display starts at 1. What is the fewest button presses needed to display 1000?