I need to know how to solve this algebra question. mr. smiths dad is 5 times as old as he was 40 years ago. how old is mr. smiths dad?

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Marked as Best Answer

Hi Tom;

I ADDED ANOTHER SOLUTION. SEE BELOW...

x=Mr. Smith's Dad's age 40-years-ago.

5x=x+40

Let's isolate x...

Let's subtract x from both sides...

-x+5x=x+40-x

4x=40

Let's divide both sides by 4...

4x/4=40/4

x=10

10+40

Mr. Smith's Dad is 50-years-old.

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You could also do...

x=Mr. Smith's age

x/5=x-40

Add 40 to both sides to isolate x...

(x/5)+40=x-40+40

(x/5)+40=x

Subtract (x/5) from both sides

-(x/5)+(x/5)+40=x-(x/5)

40=x-(x/5)

Isolate x...

40=x(1-(1/5))

Because (1-(1/5))=0.8...

40=0.8x

Divide both sides by 0.8...

40/0.8=(0.8x)/0.8

50=x

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