[Infas60]

Hello Amiya,

I have worked through the problem, and here is my understanding

total time taken,
First 20 units = 80 hours
next 10 units = 30 hours
final 10 units = 25 hours

thus, total time taken for first 40 units 135 hours

based on that average time per unit is,
20 units = 80/20 = 4hours
40 units = 135/40 = 3.375 hours

so the answer is,

R2 ×4=3.375
R = 0.84375

hope this clear your doubts. i planned to do exam in pm exam in December going through this help me as well.

[Author]

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