2460.28 – Present and Future Ages I


Sosthenes is three times as old as Benoni. Five years from now, the sum of their ages will be thirty-four years. What are their present ages?


Solution

In five years, Sosthenes and Benoni will have each gained five years for a total of thirty-four years between them. This means that the sum of their ages today is twenty-four years:

(S+5)+(B+5)=34S+B+10=34S+B=24\begin{aligned}(S + 5) + (B + 5) &= 34 \\S + B + 10 &= 34 \\S + B &= 24\end{aligned}

In addition, Sosthenes is three times as old as Benoni, S=3BS = 3 B. Therefore we can write:

3B+B=244B=24B=6\begin{aligned}3 B + B &= 24 \\4 B &= 24 \\B &= 6\end{aligned}

As Benoni’s current age is six years, Sosthenes’s current age is eighteen years.

Check: 11+23=3411 + 23 = 34.