4a+5b=7,b=8

Re: 4a+5b=7,b=8

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This says we are just letting b=8 and then trying to find "a"

OK....so

4a + 5(8) = 7

4a + 40 = 7    subtract 40 from both sides

4a = -33          divide both sides by 4

a = -33/4

That's it !!   You should check this answer in the original equation to make sure it's true.

Thanks Chris,

Our anonymous enquirer should change it to a mixed numeral i think.

I really like the way you explain these questions Chris.  I probably should try to adopt a similar method.