Question
Let A=\ (a,b,c): a,b,c are non-negative integers and a+b+2c=22\ . Then n(A) is equal to:
Let A=\ (a,b,c): a,b,c are non-negative integers and a+b+2c=22\ . Then n(A) is equal to:
C. 144
The given equation is a + b + 2c = 22, where a, b, c are non-negative integers. This can be rewritten as a + b = 22 - 2c. Since a 0 and b 0, we must have 22 - 2c 0, which gives c 11. Since c is a non-negative integer, the possible values for c are 0, 1, 2, , 11. For a fixed value of c, the number of non-negative integer solutions to the equation a + b = 22 - 2c is given by (22 - 2c) + 1 = 23 - 2c. The total number of solutions n(A) is the sum of the number of solutions for each possible value of c: n(A) = _ c=0 ^ 11 (23 - 2c) n(A) = 23 + 21 + 19 + + 1 This is an arithmetic progression with 12 terms, first term 1, and last term 23. n(A) = 12 2 (1 + 23) = 6 24 = 144 Answer: 144
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