Some of these squares are to be shaded so that:

(i) at least 2 squares are shaded

(ii) two squares meeting along an edge or at a corner are not both shaded.

**How many**ways are there to do this?

Kindly provided by UKMT The figure shown above is made from 7 small squares.
Some of these squares are to be shaded so that: (i) at least 2 squares are shaded (ii) two squares meeting along an edge or at a corner are not both shaded. How many ways are there to do this?
6 Comments
Rebeka Pali
4/5/2016 11:40:49 am
I think there are 6 ways in total: 5 to shade two squares and one to shade 3 squares.
Reply
tom
4/5/2016 03:35:13 pm
I make it 10.
Reply
Ahmad
4/5/2016 05:29:21 pm
Yes, me too it is 10 as Mr. Tom
Reply
Simon Geard
4/5/2016 09:44:11 pm
a
Reply
Simon Geard
4/5/2016 09:46:19 pm
2nd row should have been be,bf (not bd,be).
Reply
Lazarus
5/10/2016 08:22:23 pm
A few ppl struggling on the rules here, it's 21.
Reply
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