1. The problem is to express the number 0.64 with 2 significant figures (s.f.). 2. Significant figures are the digits in a number that carry meaning contributing to its precision. For 2 significant figures, we keep the first two non-zero digits. 3. The number 0.64 already has two digits, both non-zero, so it is already expressed with 2 significant figures. 4. Therefore, the number 0.64 to 2 significant figures is simply 0.64. Final answer: **0.64**