Question

Solve previous year Question of iit jee

Chapter :- sequence and series​

Answer 1

Answer:

Option (B ) ,time taken by hum to count all notes is 34min

Step-by-step explanation:

Number of notes that the person counts in 10min

= 10× 150 = 1500

Since, a₁₀ , a₁₁, a₁₂ ------- are in AP with common difference -2

Let n be the time taken to count remaining 300notes , then

• => n/2[(2×148 + (n-1)×-2] = 3000

• => n² - 149n + 3000 = 0

• => (n - 24) ( n-125) = 0

• => n = 24 , 125

neglecting n = 125 because value of a₁₂₅ will be negative which is not possible in currency note

so , Total time taken by the person to count all notes = 10 + 24 = 34min