Question

the cost of drilling a tubewell is rupees 2.50 per food for the first Hundred feet and an additional rupees 0.254 every subsequent food find the cost of the last food and the total cost of 220 feet deep tubewell​

Answer 1

Given:

For 1st 100 feet:

1st term (a) = 2.50

Common difference (d) = 2.50

n = 100

Now:

$\implies$ an = a + (n-1) d

$\implies$ an = 2.50 + (100-1) 2.5

$\implies$ an = 2.50 + 247.50

$\implies$ an = 250

Now:

Sum of 100 feet:

$\implies$ $\sf{Sn=\frac{n}{2} (a+an)}$

$\implies$ Sn = $\frac{100}{2}$ (2.50 + 250)

$\implies$ Sn = 50 (252.5)

$\implies$ Sn = 375

For the other 120 feet:

Take 1st term (a) = 2.75

Common difference (d) = 0.25

n = 120

Now:

$\implies$ an = a + (n-1) d

$\implies$ an = 2.75 + (120-1) 0.25

$\implies$ an = 2.75 + 29.75

$\implies$ an = 32.5

Now:

Sum of 120 feet:

$\implies$ $\sf{Sn=\frac{n}{2} (a+an)}$

$\implies$ Sn = $\frac{120}{2}$ (2.75 + 32.5)

$\implies$ Sn = 60 (35.25)

$\implies$ Sn = 2115

Now:

Total cost of 220 feet deep well:

$\boxed{\sf{375+2115=2490}}$

Final answer: 2490

Answer 2

Answer:

l _ 32.50, s_ 250+2,115_2,365