The correct option is: (A) Rs 4900
Explanation:
1st instalment = Rs 1000
2nd instalment = Rs1000 + Rs 100 = Rs 1100
3rd instalment = Rs 1100 + Rs 100 = Rs 1200 and so on
Let number of instalments = n
.'. 1000 + 1100 + 1200 + ... up to n terms = 118000
=> n/2[2 x 1000 + (n - 1) 100] = 118000
=> 100n2 + 1900n - 236000 = 0
=> n2 + 19n - 2360 = 0
=> (n + 59)(n - 40) = 0
.'. Total no. of instalments = 40
Now, last instalment = 40th instalment
. .. a40 = a + 39d = Rs 4900