sam_reddy

• Jun 13th, 2006

 

considering a 5 cube, there will be 3 squares for each edge which are painted on exactly 2 sides with paint. that means, 3*12 / 5^3.that is 36/ 125.however, answer changes when it is at least 2 sides... that will be 5*4 + 3*8 / 125.thats 44/125.

priyanka_m

 Profile Answers by priyanka_m 

• Nov 16th, 2006

 

  hi!

the answer is 36/125,ill explain how.......

side = 5 cm, which means volume = 5 cube = 125 cm cube

total painted surface area = 6 * (area of one face) = 6 * 25 = 150 cm square

when cube is divided into smaller cubes of side 1 cm each, in effect it means that every face of the cube is divided into 25 parts. (try drawing it)..... of these, those on the border will be painted on AT LEAST 2 sides. these are 16 in number. however, those on the corners are painted on 3 sides... these are 4 in number. so, 16-4 = 12 are painted on exactly 2 sides.

so, 12 * 6 = 72 cm square of area is painted ....

hence probabilty = 72/150 = 36/125 (answer)