A bite-size number-logic puzzle. Fill a 3×3 grid with the digits 1 to 9, each used once, so that every circle equals the sum of the four cells around it. Solve as many as you can in 90 seconds.
The grid has nine cells and four circles. Each circle sits where four cells meet and shows a target — the four cells touching it must add up to that number.
Place the digits 1 through 9, each exactly once. Tap an empty cell, then tap a digit from the pad; tap a filled cell to clear it. Given digits are locked.
A circle turns green when its four cells add up correctly and red when they are all filled but wrong, so you always see which corner is off. Fill every cell so all four circles are green to solve it.
Each solve scores a point and a fresh puzzle appears at once. Solve as many as you can before the clock runs out.
Start from the circle with the most extreme target. A corner needing a very small total must be built from low digits — 1, 2, 3 and 4 are your only tools — while a corner near the maximum is forced to use 9, 8, 7 and 6. Pinning those tight corners first strips the most options from the rest of the grid.
The centre cell is the busiest square on the board: it belongs to all four circles at once, so it is counted in every target. Work out what the middle digit must be and all four corners tighten around it; a wrong guess in the centre throws off all four sums, which is exactly why the centre is the fastest cell to confirm or rule out.
Lean on the digits you have already used. Because each number appears exactly once, every placement crosses possibilities off the pad — the greyed-out digits carry as much information as the ones on the board. When a cell has only one unused digit that can fit its circle, place it and let the deductions chain.
In the timed mode, speed comes from the givens. Read the locked digits first, find the circle they constrain the most, and fill the forced cells before you start reasoning about the open ones. A grid that looks blank is usually one confident corner away from solving itself.