Q3 of 50 Page 32

Calculate the difference between the sum of the first 20 terms of the arithmetic sequences 6, 10, 14, … and 15, 19, 23, …

Case i)


a = 6


d = 10-6 = 4


n = 20


Sn1 =


= 10×88


= 880


Case ii)


a = 15


d = 19-15 = 4


n = 20


Sn2 =


= 10×106


= 1060


The difference between the sum of the first 20 terms of the arithmetic sequences 6, 10, 14, … and 15, 19, 23, … = Sn1 – Sn2


= 1060- 880


= 180


Hence, answer is found out.


More from this chapter

All 50 →
1

Find the sum of the first 25 terms of each of the arithmetic sequences below.

1, 6, 11, …

 2

What is the difference between the sum of the first 20 terms and the next 20 terms of the arithmetic sequence 6, 10, 14, …?

 4

Find the sum of all three digit numbers, which are multiples of 9.

 5

Find n is the equation 52 × 54 × 56 × … × 52n = (0.008)-30.