Answer: 1110
Explanation:
For an arithmetic progression, the nth term is gotten by using the formula:
= a + (n-1)d
Therefore,
7th term = a + 6d = 38 ..... equation i
12 term = a + 11d = 63 ...... equation ii
Subtract equation i from ii
(a + 6d) - (a + 11d) = 38 - 63
-5d = -25
d = 25/5
d = 5
Since d = 5
From a + 6d = 38
a = 38 - 6d
a = 38 - (6×5)
a = 38 - 30
a = 8
The sum of the first 20 terms will be:
= n/2[2a + (n-1)d]
= 20/2[(2×8) + (20-1)5]
= 10[16+(19 × 5)]
= 10(16+95)
= 10(111)
= 1110