This question was previously asked in

SSC CHSL Previous Paper 87 (Held On: 12 Oct 2020 Shift 1)

Option 3 : 20 km/h

HSSC Constable Male 23rd December 2018 official paper

16067

100 Questions
80 Marks
90 Mins

**Given:**

Richa travels from A to B at the speed = 15 km/hr

Richa travels from B to C at the speed = 20 km/hr

Richa travels from C to D at the speed = 30 km/hr

AB = BC = CD

**Formula:**

Average speed = Total distance/Total time

**Calculation:**

Let AB = BC = CD = 60 km (LCM of 15, 20 and 30)

Total distance = 3 × 60 = 180 km

Time taken by Richa to travels from A to B = 60/15 = 4 hrs.

Time taken by Richa to travels from B to C = 60/20 = 3 hrs.

Time taken by Richa to travels from C to D = 60/30 = 2 hrs.

Total time taken by Richa to travels from A to D = 4 + 3 + 2 = 9 hrs.

∴ Average speed = 180/9 = 20 km/hr.