| Date | May 2013 | Marks available | 1 | Reference code | 13M.1.sl.TZ2.10 |
| Level | SL only | Paper | 1 | Time zone | TZ2 |
| Command term | Write down | Question number | 10 | Adapted from | N/A |
Question
Alan’s laundry basket contains two green, three red and seven black socks. He selects one sock from the laundry basket at random.
Write down the probability that the sock is red.
Alan returns the sock to the laundry basket and selects two socks at random.
Find the probability that the first sock he selects is green and the second sock is black.
Alan returns the socks to the laundry basket and again selects two socks at random.
Find the probability that he selects two socks of the same colour.
Markscheme
\(\frac{3}{{12}}\left( {\frac{1}{4},0.25,25\% } \right)\) (A1) (C1)
\(\left( {\frac{2}{{12}}} \right) \times \left( {\frac{7}{{11}}} \right)\) (M1)
Note: Award (M1) for correct product.
\( = \frac{{14}}{{132}}\left( {\frac{7}{{66}},0.10606...,10.6\% } \right)\) (A1) (C2)
\(\left( {\frac{2}{{12}} \times \frac{1}{{11}}} \right) + \left( {\frac{3}{{12}} \times \frac{2}{{11}}} \right) + \left( {\frac{7}{{12}} \times \frac{6}{{11}}} \right)\) (M1)(M1)
Note: Award (M1) for addition of their 3 products, (M1) for 3 correct products.
\( = \frac{{50}}{{132}}\left( {\frac{25}{{66}},0.37878...,37.9\% } \right)\) (A1) (C3)
