Hello from MrBillDoesMath!
Answer:
-137
Discussion:
It appears the 8 is subtracted from each term in the sequcnes as we proceed from left to right. The equation describing the nth terms is therefore:
a(n) = 15 - 8 * (n-1)
a(1) = 15 - 8(0) = 15
a(2) = 15 - 8*(2-1) = 15 - 8 = 7
a(3) = 15 - 8(3-1) = 15 - 8(2) = 15 - 16 = -1
etc
The 20th term is given by
a(20) = 15 - 8(20-1)
= 15 - 8 * 19
= 15 - 152
= -137
Thank you,
MrB