Ex 3.1, 8 The rainfall (in mm) in a city on 7 days of a certain week was recorded as follows: (i) Find the range of the rainfall in the above data
Maximum rainfall = 20.5
Minimum rainfall = 0.0
Range = Maximum rainfall − maximum rainfall
= 20.5 − 0.0
= 20.5
Ex 3.1, 8 (ii) Find the mean rainfall for the week
Mean rainfall = (𝑇𝑜𝑡𝑎𝑙 𝑟𝑎𝑖𝑛𝑓𝑎𝑙𝑙)/(𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑎𝑦𝑠)
Total rainfall = 0.0 + 12.2 + 2.1 + 0.0 +20.5 + 5.5 + 1.0
= 12.2 + 2.1 + 20.5 + 5.5 + 1.0
= 122/10 + 21/10 + 205/10 + 55/10 + 10/10
= ((122 + 21 + 205 + 55 + 10))/10
= 413/10
= 41.3
Thus,
Mean rainfall = (𝑇𝑜𝑡𝑎𝑙 𝑟𝑎𝑖𝑛𝑓𝑢𝑙𝑙)/(𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑎𝑦𝑠)
= 41.3/7
= 41.3 × 1/7
= 413/10 × 1/7
= 413/7 × 1/10
= 59 × 1/10
= 59/10
= 5.9
Thus, mean rainfall is 5.9 mm
Ex 3.1, 8 (iii) The rainfall (in mm) in a city on 7 days of a certain week was recorded as follows: (iii) On how many days was the rainfall less than the mean rainfall.
Mean is 5.9 mm
Here 0.0, 2.1, 0.0, 5.5, 1.0 are less than 5.9
On 5 days rainfall was less than mean rainfall.

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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