X - 7.9% = 15

[aarbar]

What formula do you use for these calculations?

 

[aarbar]

Think i've worked it out.

15 is 92.1% of the total (100 -7.9)
15 divided by 92.1 = 1%. Then multiply by 100.

 

[tkhunny]

AS WRITTEN, there isn't any of that.

x - 7.9% = 15
x - 0.079 = 15
x = 15.079

Are we SURE we're asking the right question? Perhaps the WHOLE problem statement and/or some idea of what it is you are trying to do?

 

[aarbar]

AS WRITTEN, there isn't any of that.

x - 7.9% = 15
x - 0.079 = 15
x = 15.079

Are we SURE we're asking the right question? Perhaps the WHOLE problem statement and/or some idea of what it is you are trying to do?

I probably haven't written it mathematically correct. Basically I wanted to calculate what number minus 7.9% is 15. But i managed to work it out - see my first comment. 16.29 rounded up. Because 16.29 - (7.9% of 16.29) is 15

 

[Harry_the_cat]

I probably haven't written it mathematically correct. Basically I wanted to calculate what number minus 7.9% is 15. But i managed to work it out - see my first comment. 16.29 rounded up. Because 16.29 - (7.9% of 16.29) is 15

Then your original equation would be x - 7.9% of x =15.

 

[Dr.Peterson]

Think i've worked it out.

15 is 92.1% of the total (100 -7.9)
15 divided by 92.1 = 1%. Then multiply by 100.

This is correct, given that the equation was x - 7.9%x = 15. You have correctly recognized that 100% - 7.9% = 92.1%, so you divide by 0.921.

Algebraically, what you did was:

x - 0.079x = 15​

1.000x - 0.079x = 15​

(1.000 - 0.079)x = 15​

0.921x = 15​

x = 15/0.921 = 16.29 (approx)​