Ncert Exercises & Solutions

The mass of a box measured by a grocer’s balance is 2.300 kg. Two gold pieces of masses 20.15 g and 20.17 g are added to the box. What is (a) the total mass of the box, (b) the difference in the masses of the pieces to correct significant figures?
1. \(2.338~\text {kg},~0.03~\text g\)
2. \(2.342~\text {kg},~0.02~\text g\)
3. \(2.340~\text {kg},~0.02~\text g\)
4. \(2.335~\text {kg},~0.01~\text g\)

Here, the mass of the box, m = 2.3 kg
Mass of one gold piece,m₁= 20.15 g = 0.02015 kg
Mass of other gold piece, m₂ = 20.17 g = 0.02017 kg
(a) Total mass = m + m₁ + m₂
= 2.3 + 0.02015 + 0.02017 = 2.34032 kg As the result is correct only upto one place of decimal, therefore, on rounding off total mass = 2.3 kg
(b) Difference in masses = m₂– m₁
= 20.17-20.15 = 0.02 g (correct upto two places of decimal).

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