Getting the top left corner of a grid cell (math problem)

Question

I'm making a map editor for a tile based game. The editor makes a grid:
private function drawGrid():void {
            var grid:Sprite = new Sprite();
            var tileSize:uint= 50;
            for(var i:int=0;i<row;i++)
                grid.graphics.lineStyle(1,0x000000,0.3);
                grid.graphics.moveTo(0, i*tileSize);
                grid.graphics.lineTo(700, i*tileSize);
            for(var j:int=0;j<column;j++)
                grid.graphics.lineStyle(1,0x000000,0.3);
                grid.graphics.moveTo(j*tileSize, 0);
                grid.graphics.lineTo(j*tileSize, 400);
            stage.addChild(grid);
And when the user clicks anywhere in the screen a movieclip is added to stage. The movieclip (exported for actionscript as Tile) should be placed in the top left corner of the grid cell.
private function placeTile(mouseX:int, mouseY:int, frame:uint):void {
            var tile:Tile = new Tile();
            tile.gotoAndStop(frame);
            tile.x = PROBLEM HERE
            tile.y = PROBLEM HERE
            stage.addChild(tile);
How can I do that? I came up with an idea but it didn't work because I have a math problem.  Let's pretend that the user mouse is at position mouseX = 456:
I could remove the hundreds and use the quotient 56 and check if it is above 50. If it is above 50 I would place it at x = 500 if not I would place it at x = 450. How can I remove the hundreds? Do you have a better idea?
Message was edited by: wilsonsilva7 because unconsciously I pressed ctrl+s (to save) and the message was posted

Answer 1

Thanks. I asked a friend and he told me about the %but I still had a problem. Your expression solved my problem
        private function placeTile(mouseX:int, mouseY:int, frame:uint):void {
            var tile:Tile = new Tile();
            tile.gotoAndStop(frame);
            tile.x = Math.floor(mouseX / tileSize) * tileSize;
            tile.y = Math.floor(mouseY / tileSize) * tileSize;
            stage.addChild(tile);
That way every tile is centered every 50 pixels