# Civil Engineering - Water Supply Engineering - Discussion

### Discussion :: Water Supply Engineering - Section 7 (Q.No.5)

5.

The population of a city in 2000 is 50,000. The average increase in population over last 8 decades is 7500 and average incremental increase during 8 decades is 750. The population of the city based on incremental method, in the year 2020 will be

 [A]. 55,000 [B]. 60,500 [C]. 66,500 [D]. 72,500 [E]. 76,500

Explanation:

No answer description available for this question.

 Jajhjiik said: (Aug 14, 2015) According to incremental increase method, yn = yo+nr+n(n+1)/2xk. yo = Initial population n = No of decades k = net incremental increase. r = avg increase in population. So, y 2020 = 50000+7500x2+3x750 = 67250. Answer given is wrong.

 Grace said: (Mar 29, 2017) By incremental increase method, Pn = P + n (Average Increase+ Incremental Increase) Given: P=50,000 ; n=2 ; Average Increase = 7500 ; Incremental Increase = 750, Hence P2=50000+2(7500+750) = 66,500.

 Ghosh said: (Nov 14, 2017) Yes 67250 is the right answer here.

 Satish Verma said: (Apr 18, 2018) 67250 is the right option.

 Jignesh said: (Sep 5, 2018) @Jajhjiik. Can you please explain how came 2 ad 3?

 Girma B. said: (Feb 26, 2019) The final answer is 67250.

 Subhasmita Patra said: (Jul 14, 2019) The formula for geometrical increase method is; P(1+IG/100)^n. P= population. IG= average percentage per decade. n= no of decad. So, Pn=50000(1+20/100)^2. = 72000.

 Mahesh Sinh said: (Mar 31, 2020) Pn = P+n(Ia+Iinc), Pn = 5000+2(7500+750). = 66500.

 Prashanth said: (Apr 20, 2020) @Jajhjiik. How it came 3? please explain sir.

 Renis@Gajipara said: (Aug 26, 2020) The population of the city based on the incremental method, in the year 2020. i = 7500 & r = 750. Pn = P + (i+r)n. = 50000 + (7500+750)*2. Pn = 66500. Where, P = Present population in 2000. i = avg. increase in population. r = avg. incremental increase. n = Number of decades.

 Pooja said: (Sep 11, 2020) Pn = Po + nx + [(n(n+1))/2]*y. n = no Of decades, x = avg increase in population, y = avg. incremental increase, Po = initial population.

 Anirban Roy said: (Sep 23, 2020) Yes, you are right @Pooja. So, Pn = 55000 + 2 * 7500+(2 * 3÷2) * 750 = 67250.

 Noini said: (Dec 3, 2020) Avg increase is 7500 calculated for 8 decades. Then the total increase in population from 1930 is 7500x8=60000. If increase itself is 60000, what is the actual population in 1920 initially then? How can the population in 2000 be very less=50000? Please anyone explain.

 Smith said: (Dec 24, 2020) Thanks all for eplaining the answer.