Question

A tube well is bored 80 meters deep. The 1st meter costs ₱1250 and the cost per meter increases by ₱250 for every subsequent meter. Find the cost of boring the 75th meter and the total cost incurred for the entire job.

Answer 1

the cost of boring the 75th meter  = ₱ 19750 & Cost of Entire job = ₱ 890000

Step-by-step explanation:

Cost for 1st meter = ₱ 1250

a = 1250

d = 250

Cost for 75th meter  

= a + (75 - 1)d

= a + 74d

= 1250 + 74 * 250

= 1250 + 18500

= 19750

the cost of boring the 75th meter  = ₱ 19750

Total cost for 80 m

n = 80

80th meter cost  = a + (80-1)d  

= 1250 + 79*250

= ₱ 21000

Sum = (80/2)(1250 + 21000)

= 40 * 22250

= 890000

Cost of Entire job = ₱ 890000

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