Explanation:

Sol. Ans.(b).

Start directly from the options.

Option (a) – Rs.30. Hike it by 25% and it becomes Rs.37.5 per kg. Originally one could buy (1200 / 30) = 40 kg rice and now one can buy (1200 / 37.5) = 32 kg. Difference is 8 kg and not 6 kgs.

Option (b) – Rs.40. Hike it by 25% and it becomes Rs.50 per kg. Originally one could buy (1200 / 40) = 30 kg rice and now one can buy (1200 / 50) = 24 kg. . Difference is 6 kg and (b) is our answer.

Other method: Let the original price be P. So, 1.25 P is the new price.

Earlier quantity purchased = 1200 / P kg.

New quantity purchased = 1200 / 1.25P kg

Difference = 6 kg = 1200/P – 1200/1.25P.

Solve for P.