JEE Advance - Mathematics (1982 - No. 24)
In a certain test, $${a_i}$$ students gave wrong answers to atleast i questions, where i = 1, 2,..., k. No student gave more than k wrong answers. The total number of wrong answers given is.....................................
$$k * a_k$$
$$\sum_{i=1}^{k} i * a_i$$
$$\sum_{i=1}^{k} a_i$$
$$\prod_{i=1}^{k} a_i$$
$$k!$$