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topkids
07-20-2011, 10:02 PM
please help! A proffessor is three times as old as one of his pupil. four years ago he was four times as old as freddie was at that time? how old is freddie?

soroban
07-21-2011, 06:57 PM
Hello, topkids!


A professor is three times as old as Freddie.
Four years ago, he was four times as old as Freddie at that time.
How old is Freddie?
\text{Let }x\text{ = Freddie's age now.}
\text{Then }3x\text{ = prof's age now.}

\begin{array}{c}\text{Four years ago, they were both 4 years younger.}\\ \text{Freddie's age was }x-4 \\ \text{The prof's age was }3x-4 \end{array}

\text{At that time: }\:\underbrace{\text{prof's age}}_{3x-4} \; \underbrace{\text{was}}_{=} \; \underbrace{\text{4 times}}_{4\;\times} \; \underbrace{\text{Freddie's age}}_{x-4}

\text{There is our equation! }\quad 3x-4 \:=\:4(x-4)