Question

In an Ap 5th term is 26 and 10th terms is 51 find the Ap then find s20

Answer 1

Given: a+4d = 26             -(1) a+9d = 51              -(2) On subtracting eq. (1) from eq. (2) we get: 5d=25 d=5 Putting d = 5 in eq. (1) we get: a=6 Now, a=6 and d =5 So, a20=a+19d                            =6+19×5                                    =6+95                            =101 Hence, the 20th term of the given AP is 101.