# Guesstimate Example # 9 | How many signals are red at this particular moment in Kolkata?

#### Q. How many signals are red at this particular moment in Kolkata?

Assuming average peak city hour when all signals are functioning normally

Traffic Signal color duration:
Red – 45% of the time
Green – 45% of the time
Yellow – 10% of the time

Area of Delhi = 1400 sq km (known by knowledge)

Area of Kolkata = 300 sq km = 3×10^8 sq m (assumed by comparison)

By Govt. suggested City Planning, 20% area of a city should be roads

Total area of roads = 0.2x3x10^8 = 6×10^7 sq m

Width of road = 40m

Length of roads = [6×10^7 sq m]/40m = 2×10^6 m

A signal is present every 400m

Total no. of signals in Kolkata = [2×10^6 m]/400m = 5,000

Total no. of signals Red at any point of time:

0.45×5000 = 2250 = rounded to= 2500 signals

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