Question

The number of bacteria in a certain culture doubles every hour. If there were 30 bacteria present in the culture originally, how many will be present at the end of 4″ hour?
(A) 120
(B) 240
(C) 480
(D) None of these

Answer 1

Number of Bacteria present in the culture form GP whose 1st term (a) = 30 and common ratio (r) = 2.

∵ Tn = arⁿ⁻¹

so,

Bacteria present after 2nd hour(a₃) = ar² = 30(2)²= 120

Bacteria present after 4 hour(a₅) = ar⁴ = 30(2)⁴ = 480

Bacteria present after nth hour = arⁿ = 30(2)ⁿ

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Answer 2

A)120
Hoping it will help you