JB Sequence Formulae

Question 1

nth term in AP

Answer 1

a + (n-1)d

Question 2

sum of n terms in AP

Answer 2

(n/2) x (first term + last term)
or
(n/2) x (2a + [n-1]d)

Question 3

number of terms b/w 5 and 9

Answer 3

last - first - 1
= 9 - 5 -1
= 3

Question 4

number of terms b/w 5 and 9, inclusive

Answer 4

last - first + 1
= 9 - 5 + 1
= 5

Question 5

number of terms from 5 to 9

Answer 5

last - first + 1
= 9 - 5 + 1
= 5

Question 6

number of terms from 5 to 9, exclusive

Answer 6

last - first - 1
= 9 - 5 -1
= 3

Question 7

nth term in GP

Answer 7

a x r^(n-1)

Question 8

Sum of n terms in GP

Answer 8

a x ([1- r^n] / [1 - r])

Question 9

Sum of n terms in HP

Answer 9

(middle term) x n