Question

Awarding 90 Points

Answer 1

Answer:

• 1090

Step-by-step explanation:

Given AP

• a₁₂ = 62
• a₂₀ = 102

To find

• S₂₀

Solution

• a₁₂ = a + 11d = 62
• a₂₀ = a + 19d = 102

Subtract the first equation from the second one:

• 8d = 40
• d = 5

Find a:

• a + 11*5 = 62
• a = 62 - 55
• a = 7

Find the sum of the first 20 terms:

• S₂₀ = 1/2*20(a + a₂₀) = 10(7 + 102) = 10(109)= 1090