Q.Round off each of the following quantities to three significant figures : a. 1.43 cm3 b. $458 \times 10^2$ cm c. 643 cm2 d. 0.039 m e. $6.398 \times 10^{-3}$ km f. 0.0179 g g. 79,000 m h. 42,150 i. 649.85 j. 23,642,000 mm k. 0.0041962 kg

a. 1.43 cm3 already has exactly 3 significant figures → 1.43 cm3 (unchanged).

b. $458 \times 10^2$ cm = $4.58 \times 10^4$ cm, already 3 sig figs → $4.58 \times 10^4$ cm.

c. 643 cm2 already 3 sig figs → 643 cm2 (unchanged).

d. 0.039 m — expressed to 3 significant figures: 0.0390 m (i.e. $3.90 \times 10^{-2}$ m).

e. $6.398 \times 10^{-3}$ km — keep '6.39', next digit 8 (≥5) rounds up: 6.40, giving $6.40 \times 10^{-3}$ km.

f. 0.0179 g already has exactly 3 sig figs (1, 7, 9) → 0.0179 g (unchanged).

g. 79,000 m expressed to 3 sig figs: $7.90 \times 10^4$ m.

h. 42,150 — keep '421', next digit 5 (≥5) rounds up: 422, giving $4.22 \times 10^4$.

i. 649.85 — keep '649', next digit 8 (≥5) rounds up: 650. …

For each quantity, identify the first 3 significant digits, then round the third one up or leave it uncha …

• For (d) and (g), forgetting that rounding to MORE sig figs than a plain decimal shows (0.039 → 3 sf) means padding with a zero that represents the assumed precision, not discovering new information. …