Diketahui [tex] \frac{ 5^{3x} }{25^y} = 3125 [/tex] dan [tex] 2^{x}. 4^{y-1} = 32[/tex] maka nilai x+y adalah...

jawab
5^(3x) / 25^(y) = 3.125
5^(3x) / 5^(2y) = 5^5
5^(3x - 2y) = 5^5
3x - 2y = 5 

2^x. 4^(y-1) = 32
2^x. 2^2(y-1) = 2^5
x + 2(y - 1) = 5
x + 2y - 2 = 5
x + 2y = 7

3x - 2y = 5
x +  2y = 7 | (+)
4x = 12
x = 3

x + 2y = 7
3 + 2y = 7
2y = 4
y = 2

x + y = 3 + 2 = 5