AlgebraWORD PROBLEMSExample 4:A man is 21 years older than his son. Five years ago he was four times as old as his son.How old is each now?Solution:Step 1. Let x = Son’s Age NowStep 2. Then,x + 21 = Father’s Age Nowx - 5 = Son’s Age Five Years Ago(x + 21) - 5 = Father’s Age Five Years AgoStep 3. Five years ago the father was four times as old as his son.(x + 21) - 5 = 4(x - 5)Step 4. (x + 21) - 5 = 4(x - 5)x + 16 = 4x - 20x - 4x = -20 - 16-3x = -36x = 12 yearsSolving for the other unknowns:x + 21 = 12 + 21x + 21 = 33 yearsAnswers: Son’s Age Now = 12 yearsFather’s Age Now = 33 yearsStep 5. The man is 21 years older than his son.12 + 21 = 33 yearsFive years ago he was four times as old as his son.33 - 5 = 28 = 4(12 - 5) = 4 x 7Thus, the answers check.Rev. 0 Page 49 MA-02
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