Solving Sudoku puzzles made easy (part 4)

There's only one place that the 4 can go in the top row, so do that.

We're now doing row three, missing numbers 1,2 and 9.
There's only one place for the 2 (it can't go in the middle-top box).
That leaves you with only one place in row three where the 9 can go (because there's already a 9 in column six in the middle-bottom box), so you then do the 1 as well.

Having noted (in part 3) where various 2s and 9s could go, and having just entered a 2 in the top-left box, we know that the cell marked "2,9" must be a 9, so do that, then we also know where the 2 goes in the middle-left box, so do that, and we also know where the 9 goes in that box.

That leaves us with 5 and 8 to insert in the top-middle box. There's already an 8 in column six (middle-bottom box) so do the 8 and then the 5.

Next, we'll attack row 2, so write down the missing numbers 1,2 and 6 in the margin at the left.

Full series here.