Question

Please help, (AP is arithemtic progression)

Answer 1

Answer:

p = 8

Step-by-step explanation:

The n th term of an AP is

$a_{n}$ = a₁ + (n - 1)d

where a₁ is the first term and d the common difference

Given a₉ = 4 + 5p and d = 5, then

a₁ + 8d = 4 + 5p, that is

a₁ + 8(5) = 4 + 5p

a₁ + 40 = 4 + 5p ( subtract 40 from both sides )

a₁ = 5p - 36

a₂ = 5p - 36 + 5 = 5p - 31

a₃ = 5p - 31 + 5 = 5p - 26

a₄ = 5p - 26 + 5 = 5p - 21

Given that the sum of the first 4 terms = 7p - 10, then

5p - 36 + 5p - 31 + 5p - 26 + 5p - 21 = 7p - 10, that is

20p - 114 = 7p - 10 ( subtract 7p from both sides )

13p - 114 = - 10 ( add 114 to both sides )

13p = 104 ( divide both sides by 13 )

p = 8