"Banana Kingdom uses only two types of coins, i.e. 5-cent coin and 21-cent coin. Because of this, some numbers cannot be paid using only these two types of coins. For example, 6 cents, 7 cents, 22 cents.... etc. What is the biggest number that cannot be paid by using these 2 types of coins? Assume that there are indefinite supply of coins"
At a first glance, I would think the answer is infinite, but that's wrong. Answer should be 79. This question is difficult, but very doable.
To me, this book is among the best for this reason. Many people cannot do this just because they are impatient. If I show them and get them to list down the numbers that can be paid by those coins, most people can get the answer. My son understands after I show him the answer. However, he does not know how to explain this well to others. I encourage him to do so to sharpen his skill. Many of the questions here need analytical skill. Worth considering if you kids like Maths. I would like to thank the author, Ms Loh Cheng Yee, for her good work. I think Ms Loh's books are pretty good.
By the way, for those not familiar with Singapore, GEP stands for Gifted Education Program. This program is designed for top students in Singapore. I heard that some parents send their kids to tuition with hopes that they get into this program. I discourage such attitude because the kids will suffer and will drop out. Similarly, many parents buy Olympiad Maths book for their kids and even pay for expensive Olympiad Math Training with the hope that their kids will win in Olympiad Math competition. I disagree with such attitude too. I hope you don't do buy this book with such intention.
For me, I encourage my son to do this as a hobby. If he does not know the answer, he will look at the answer provided at the back and figure out how to get the answer. I am glad that my son enjoy thinking and analyzing. Usually he will share with me those difficult questions.
It is my hope that this book will help me to train my son to think and to analyze.
