Problems

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Found: 2624

Liam saw an unusual clock in the museum: the clock had no digits, and it’s not clear how the clock should be rotated. That is, we know that 1 is the next digit clockwise from 12, 2 is the next digit clockwise from 1, and so on. Moreover all the arrows (hour, minute, and second) have the same length, so it’s not clear which is which. What time does the clock show?

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Two circles are tangent to each other and the smaller circle with the center A is located inside the larger circle with the center C. The radii CD and CE are tangent to the smaller circle and the angle DCE=60. Find the ratio of the radii of the circles.

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For positive real numbers a,b,c prove the inequality: (a2b+b2c+c2a)(ab2+bc2+ca2)9a2b2c2.

Let C1 and C2 be two concentric circles with C1 inside C2 and the center A. Let B and D be two points on C1 that are not diametrically opposite. Extend the segment BD past D until it meets the circle C2 in C. The tangent to C2 at C and the tangent to C1 at B meet in a point E. Draw from E the second tangent to C2 which meets C2 at the point F. Show that BE bisects angle FBC.

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Due to a mistake in the bakery, a cake that was supposed to be shaped as two concentric pieces (like on the right diagram below) came out like the left diagram below. Find the smallest number of pieces the cake should be cut into in order to rearrange the pieces into the cake on the right side of the picture.

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Note that the cake is not tiered like a wedding cake, but is shaped like a cylinder with a flat top. Curved cuts are allowed.

Katie and Charlotte had 4 sheets of paper. They cut some of the sheets into 4 pieces. They then cut some of the newly obtained papersheets also into 4 pieces. They did this several more times, cutting a piece of paper into 4. In the end they counted the number of sheets. Could this number be 2024?

There is a scout group where some of the members know each other. Amongst any four members there is at least one of them who knows the other three. Prove that there is at least one member who knows the entirety of the scout group.

The distance between two villages equals 999 kilometres. When you go from one village to the other, every kilometre you see a sign on the road, saying 0999,1998,2997,...,9990. The signs show the distances to the two villages. Find the number of signs that contain only two different digits. For example, the sign 0999 contains only two digits, namely 0 and 9, whereas the sign 1998 contains three digits, namely 1, 8 and 9.

Two players are playing a game. The first player is thinking of a finite sequence of positive integers a1, a2, ..., an. The second player can try to find the first player’s sequence by naming their own sequence b1, b2, ..., bn. After this, the first player will give the result a1b1+a2b2+...+anbn. Then the second player can say another sequence c1, c2, ..., cn to get another answer a1c1+a2c2+...+ancn from the first player. Find the smallest number of sequences the second player has to name to find out the sequence a1, a2, ..., an.

The letters A, R, S and T represent different digits from 1 to 9. The same letters correspond to the same digits, while different letters correspond to different digits.
Find ART, given that ARTS+STAR=10,T31.