The value of a30 – a20 for the A.P 2,7,12,17,….. is (CBSE 2011)

We know:an = a + (n – 1)dd = 7 – 2= 5So,a30 – a20 = a + (30 -1 ) d – ( a + (20 – 1)d)= a + 29 d – a – 19d= 10d= 10× 5= 50

Q3 of 84 Page 5

The value of a₃₀ – a₂₀ for the A.P 2,7,12,17,….. is (CBSE 2011)

We know:

a_n = a + (n – 1)d

d = 7 – 2

= 5

So,

a₃₀ – a₂₀ = a + (30 -1 ) d – ( a + (20 – 1)d)

= a + 29 d – a – 19d

= 10d

= 10× 5

= 50

If the common difference of an A.P. is 3, then a₂₀ – a₁₅ is (CBSE 2011)

In an AP, if d = -2, n = 5 and a_n = 0, then the value of a is (CBSE 2011)

If nth term of an A.P. is (2n + 1), what is the sum of its first three terms? (CBSE 2012)

The sum of first 20 odd natural numbers is: (CBSE 2012)