2 years, 4 months ago
Which amounts up to 1 sterling pound cannot be paid exactly with fewer than 6 coins?
It is from my Maths book and I can't answer it.
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M$1 Answer
There are 4 such amounts:
88 = 50 + 20 + 10 + 5 + 2 + 1
89 = 50 + 20 + 10 + 5 + 2 + 2
98 = 50 + 20 + 20 + 5 + 2 + 1
99 = 50 + 20 + 20 + 5 + 2 + 2
Think of the total coins as being the ones needed to make the singles digit and the tens digit.
1 = 1
2 = 2
3 = 2 + 1
4 = 2 + 2
5 = 3 + 2
6 = 5 + 1
7 = 5 + 2
8 = 5 + 2 + 1
9 = 5 + 2 + 2
So the only combinations that need more than 5 need 8 or 9 in both the first and last digit.
Good luck !
88 = 50 + 20 + 10 + 5 + 2 + 1
89 = 50 + 20 + 10 + 5 + 2 + 2
98 = 50 + 20 + 20 + 5 + 2 + 1
99 = 50 + 20 + 20 + 5 + 2 + 2
Think of the total coins as being the ones needed to make the singles digit and the tens digit.
1 = 1
2 = 2
3 = 2 + 1
4 = 2 + 2
5 = 3 + 2
6 = 5 + 1
7 = 5 + 2
8 = 5 + 2 + 1
9 = 5 + 2 + 2
So the only combinations that need more than 5 need 8 or 9 in both the first and last digit.
Good luck !
source(s):
Number partitions - experience as a Math Teacher
Number partitions - experience as a Math Teacher
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