Permutations and Combinations

Question

# Solve the equation 1 + 6 + 11 + 16 + ........ + x = 148

The given equation is : 1 + 6 + 11 + 16 +...........+x = 148
Here, a = 1, d = 6 -1 = 5, l = x, Let x be the nth term

∴
or
or
or             n[2 + 5n - 5] = 296
or             n (5n - 3) = 296
or
or
n = 8                         (∵ n is a natural number)

∴                or      a + (8 -1)d = x   or 1+7 (5) = x            or x = 36