Express the following sums using sigma notation: 5 + 7 + 9 + 11 + ... + 99

a) ∑_(n=3)^(50) 2n-1
b) ∑_(n=1)^(50) 2n-1
c) ∑_(n=5)^(50) 2n-1
d) ∑_(n=1)^(25) 2n-1