Question

12. Tina hanged 20 lanterns at an equal distance apart on a string as shown below. The distance between the 1st lantern and the 5th lantern is 80 cm. Find the distance between the 1st and the last lantern.​

Answer 1

an equal distance = arithmetic sequence

xn= a+d(n-1)⇒ x₁ = a

x₅ - x₁ = 80

x₁ + 4d - x₁ = 80

4d = 80

d = 20 cm

x₂₀ - x₁ = x

x₁ + 19d - x₁ = x

19d = x

19.20 = 380