Let's Make Number Place (Elementary course)
Let's Make Number Place : Step 2
3. Fill in 7s.
There are 7s in the two columns to the right, shown in pink lines. Now, our policy is not to put 7s in the exposed cells. Then, a 7 can be in either cell A or B.
Firstly, give a try and put a 7 in cell A. To do that, a 7 must be placed on either exposed cell C or D. However, since there are 7s above cell C and above cell D, you cannot place 7s in either or them. This is no good.
So, we must put a 7 on cell B instead of cell A. There are three exposed cells on the pink horizontal line. For a try, fix 7 on the middle one.
Since we fixed the 7, no 7s cannot be placed on any cells on the pink lines. Now let's consider 3x3 "block"s as shown in green dotted lines. Following the policy to avoid exposed cells, two 7s can be placed on the marked cells.
Since we've fixed eight 7s, the rest one 7 is automatically fixed.
So we have set all 7s, with four of them exposed.
Now that 7s are completed, let's have a coffee break.
