Barry has 4 wooden blocks, 2 are blue, 1 is red and 1 is green. How many ways can he arrange the 4 blocks in a line?
Barrys friend billie is colour blind and cannot distinguish betwwen red and green. How many ways can the blocks be arranged so that billie can see different looks.
+118609 Barry has 4 wooden blocks, 2 are blue, 1 is red and 1 is green. How many ways can he arrange the 4 blocks in a line?
4!/2!=12 ways
Barry's friend Billie is colour blind and cannot distinguish between red and green. How many ways can the blocks be arranged so that Billie can see different looks?
4!/2!2! = 6 ways
+118609 Fair enough,
I do not know what you know unless you tell me, which you now have. 
If you have not studied any probability formally then you will have to just set out all the possibilities in an organized way.
Barry has 4 wooden blocks, 2 are blue, 1 is red and 1 is green. How many ways can he arrange the 4 blocks in a line?
BBRG
BBGR
GBBR
RBBG
RGBB
GRBB
BRBG
BGBR
BRGB
BGRB
RBGB
GBRB
THERE IS YOUR 12.
Barry's friend Billie is colour blind and cannot distinguish between red and green. How many ways can the blocks be arranged so that Billie can see different looks?
Now copy out those 12 choices. Bille sees red and green as the same so Chang all the R's and Gs to S (for same)
Now see how many of them are distinguishable. There should be 6.
