Three significants, both when multiplying (2.44*10+3), dividing (1.74) and substracting (27.85 = 27.9, one decimal) and four significant numbers when adding up (102.65 = 102.7, one decimal)
Four: All the digits given are significant.>> Two actually. Trailing zeros in a number without a dp are not significant unless emphasised in some way. The unit (mm) doesn't make any difference.