Answer: Option B
Answer: (b)Total weight 12 parcels = 12 × 1.8 = 21.6 kg. New average of 13 parcels = 1.8 – 0.05 = 1.75 kg. Total weight of 13 parcels = 13 × 1.75 = 22.75 kg. ∴ Weight of new parcel = 22.75 – 21.6 = 1.15 kg. Aliter : Using Rule 18, ( If in the group of N persons, a new person comes at the place of a person of 'T’ years, so that average age, increases by 't’ years Then, the age of the new person = T + N.t. ) Here, T = 1.8, N= (12 + 1) = 13, t = $50/1000$ = .05 Weight of new parcel = T – Nt = 1.8 – 13 × 0.05 = 1.8 – 0.65 = 1.15 kg