Consider the following sequence:
- Find the sum of 2 + 6 + 10 + 14 + ... + 74.
- A given line of the sequence is as follows: 2 + 6 + 10 + 14 + ... + s = 722 = 2 x t2. Find the value of t.
- Calculate the sum of Line 25 if the pattern for the sum of the lines is as follows:-
Line 1: 8
Line 2: 8 + 10
Line 3: 8 + 10 + 12
(a)
Sum of 1 number:
2 =
2 x
12Sum of 2 numbers:
2 + 6 = 8 =
2 x
22Sum of 3 numbers:
2 + 6 + 10 = 18 =
2 x
32 Sum of 4 numbers:
2 + 6 + 10 + 14 = 32 =
2 x
42
Formula:
Sum of numbers =
2 x
Number of numbers in the string2
To find out how many numbers are in the string if 74 is the last number.
Last number in sum of 1 number:
2 = 1 x 4 - 2
Last number in sum of 2 numbers:
6 = 2 x 4 - 2
Last number in sum of 3 numbers:
10 = 3 x 4 - 2
Last number in sum of 4 numbers:
14 = 4 x 4 - 2
Formula:
Last number =
Number of numbers in the string x 4 - 274 = Number of numbers x 4 - 2
74 + 2 = Number of numbers x 4
76 = Number of numbers x 4
Number of numbers
= 76 ÷ 4
= 19
Sum of 19 numbers
= 2 x Number of numbers in the string
2
= 2 x 19
2= 2 x 19 x 19
= 2 x 361
= 722
(b)
2 x t
2 = 722
t
2 = 722 ÷ 2
t
2 = 361
t = √361
t = 19
(c)
Pattern for the sum of the lines
Line
1: 8 =
2 x (
1 + 1)
2 Line
2: 8 + 10 = 18 =
2 x (
2 + 1)
2 Line
3: 8 + 10 + 12 = 32 =
2 x (
3 + 1)
2 Formula:
Sum of Line Number =
2 x (
Line Number + 1)
2Sum of Line
25 =
2 x (
25 + 1)
2 = 2 x 26
2 = 2 x 26 x 26
= 1352
Answer(s): (a) 722; (b) 19; (c) 1352