You try a few,

Problem 1: How many significant digits does the number 12,000 have?

Problem 2: How many significant digits does the number .0011 have?

Problem 3: How many significant digits does the number 12.000130 have?

Problem 4: If 120 cm and .5 cm were multiplied, how many sinificant digits should be in the answer?

Problem 5: Write the product of 52 cm and 121.5 cm using the correct number of sigificant digits.