Explanation:
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)