Question

The cost of boring a tube well 600 metres deep is as follows: 25 paise for the first metre and an additional 4 paise for every subsequent metre. Find the cost of boring 500th metre and also the total cost.

Answer 1

Total depth = 600 metre means n = 600

for 1st metre= 25 paise

for 2nd metre= 29 paise..... and so on

price difference between each metre = 4 means d= 4

first term a = 25

series = 25 , 29, 33, 37, .........

for n = 500

Sum = n/2 [ 2a+(n-1).d ]

500/2 [ 2×25+499×4] = 500/2[ 50+1996]

= 500×2046/2 = 511500 paise = 5115 Rs

in the same way

for n= 600

2446× 300 = 733800 paise = 7338 Rs.

Answer 2

Answer:

please folllow me and mark me brainilist

Total depth = 600 metre means n = 600

for 1st metre= 25 paise

for 2nd metre= 29 paise..... and so on

price difference between each metre = 4 means d= 4

first term a = 25

series = 25 , 29, 33, 37, .........

for n = 500

Sum = n/2 [ 2a+(n-1).d ]

500/2 [ 2×25+499×4] = 500/2[ 50+1996]

= 500×2046/2 = 511500 paise = 5115 Rs

so,

for n= 600

2446× 300 = 733800 paise = 7338 Rs.