An algebra problem by harsh bafna

6*x = 30 * 5
x = 150/6
x = 25

I calculated this mentally. It took me less than a second.

$\frac{5}{6}$ x $30$ = $x$ = $25$

solution is below

(6x10)/2=30 so (5x10)/2=25

ans: 25

or

6x5=30 so 5x5=25

but I am confused because I was thinking 20 as a right answer. reason is

since (6*(6-1))=30

so (5*(5-1))=20

or

6*6-6=30

so 5*5-5=20

I do not know what is right answer