Pls chk the image
Reading this question reminded me of something that I like to tell my students:
"When you solve a question, don't just solve that question. Think what you would have done had the question been a little different. Apply as many different variations as you can and try to solve each. That will help you build concept."
e.g. they have made the question a little simpler by giving you that you need numbers with 2 in the hundred's place. What if the question asked for numbers with a 2 (in any place) or numbers with only one 2 (in any place) etc.
The more you analyze the problems, the better you will get at answering tougher questions.
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