Let's say you had something like 0.4 * 0.67. You could think of 0.4 as 4/10, and 0.67 as 67/100. Then, just multiply 4*67: 4*60 = 240, + 4*7=28 --> 240 + 28 = 268. Then, multiply the denominators: 1/10 * 1/100 = 1/1000. Combine the two to get 268/1000 = 0.268.
Hope this helps.
