What are some ways to get 12 by adding 4 numbers together. I need at least 4 ways, and can only use numbers 1-9 only twice. I'm
2 answers:
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Step-by-step explanation:
Let the two-digit number is
<u>This can be written as:</u>
- 10x + y, where 1 ≤ x ≤ 9 and 0 ≤ y ≤ 9
<u>The difference between the number and product of its digits is:</u>
- d = 10x + y - xy
<u>Rewrite this as below:</u>
d = 10x - xy + y - 10 + 10 =
x(10 - y) - (10 - y) + 10 =
(x - 1)(10 - y) + 10
<u>We see that:</u>
- 0 ≤ x - 1 ≤ 8 according to the condition given above
- 1 ≤ 10 - y ≤ 10 again according to the condition given above
<u>The value of d is then:</u>
- 0 + 10 ≤ d ≤ 8*10 + 10
- 10 ≤ d ≤ 90