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Mary’s age is 3 more than twice her brother’s age. The sum of their ages is 33. What is Mary’s age?
Let Mary's and her brother's ages be M and B, respectively
Then we get: M = 2B + 3 ---- eq (i)
Also, M + B = 33____B = 33 - M ----- eq (ii)
M = 2(33 - M) + 3 ----- Substituting 33 - M for B in eq (i)
M = 66 - 2M + 3
M + 2M = 66 + 3
3M = 69
Mary's age, or 