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Question 14 Marks
In a bacteria culture under observation in a laboratory, the population of 50 bacteria doubles itself every hour.
Q.1. Which of the following expressions gives the bacterial population after n hours?
(a) $\frac{50}{2^n}$$\quad$$\quad$ (b) $25^n$ $\quad$$\quad$(c) $50 \times 2^n$$\quad$$\quad$ (d) $\frac{50^n}{2}$
Q.2. The population size of the bacteria after 3 hours will be
(a) 200 $\quad$$\quad$(b) 300 $\quad$$\quad$(c) 400 $\quad$$\quad$(d) 500
Q.3. How many bacteria will be there in the culture after 1 day?
(a) $\frac{50}{2^{12}}$ $\quad$$\quad$(b) $50 \times 2^{24}$$\quad$$\quad$ (c) $50 \times \times 2^{12}$ $\quad$$\quad$(d) $\frac{50}{2^{24}}$
Q.4. If the culture is observed after every one hour, find the number of hours after which the population size of the bacteria will be larger than 1000.
(a) 5 $\quad$$\quad$(b) 6 $\quad$$\quad$(c) 8 $\quad$$\quad$(d) 10
Answer
1. (C)
2. (C)
3. (B)
4. (A)
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Question 24 Marks
A computer purchased for ₹ 72900 loses two-third of its value every year. Its value is evaluated at the end of every year.
Q.1. Which of the following expressions gives the value of the computer (in ₹) after n years?
(a) $\frac{72900}{\left(\frac{2}{3}\right)^n}$ $\quad$$\quad$(b) $\frac{2^n \times 27900}{3^n}$ $\quad$$\quad$(c) $\frac{72900}{3^n}$ $\quad$$\quad$ (d) $\frac{72900}{2^n \times 3^n}$
Q.2. Find the value of the computer after 3 years.
(a) ₹ 8100 $\quad$$\quad$(b) ₹ 2430 $\quad$$\quad$(c) ₹ 5600$\quad$$\quad$ (d) ₹ 2700
Q.3. In how many years will the value of the computer be less than ₹ 200?
(a) 6 years $\quad$$\quad$(b) 7 years $\quad$$\quad$(c) 8 years $\quad$$\quad$(d) 10 years
Q.4. By how much will the value of the computer reduce in 4 years?
(a) ₹ 24300 $\quad$$\quad$(b) ₹ 1800 $\quad$$\quad$(c) ₹ 8100 $\quad$$\quad$(d) ₹ 72000
Answer
1. (C)
2. (D)
3. (A)
4. (D)
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[4 marks sum] - MATHS STD 7 Questions - Vidyadip