The first 10 words cost 6 naira.
The remaining 5 words cost 5 x 45k = 225k.
225k is equivalent to 0.225 naira.
Therefore, the total cost of the telegram is 6 + 0.225 = 6.225 naira. Answer: \boxed{6.225}.
If the charge for an external telegram is 6 naira for first ten words and then 45k per word for each additional word, what is the cost of a telegram of 15 words?
1 answer