Question on: WAEC Mathematics - 2008

2ⁿ = 128

2ⁿ = 2⁷

n = 7

(2^{n - 1})(5^{n - 2}) = (2^{n - 2}.2)(5^{n - 2}) put n = 7

(2^{n - 1})(5^{n - 2}) = 2(2^{n - 2} x 5^{n - 2})

= 2(2 x 5)^{n - 2}

= 2(10^{n - 2}) put n = 7

(2^n-1)(5^n-2) = 2(10⁵)