Let a=2,4,6,...,100 and b=1,3,5,...,99
Let
a+b=23λ+2
If λ=1, then
a+b=25
So, (1,24),(3,22),....,(23,2)
Total ordered pairs=12
If λ=2, then
a+b=48
No ordered pair possible.
If λ=3, then
a+b=71
So,
(1,70),(3,68),(5,66),....,(61,10),(63,8),(65,6),(67,4),(69,2)
Total 35 ordered pairs.
If λ=5, then
a+b=117
(17,100),(19,98),...,(99,18)
Total 42 ordered pairs.
If λ=7, then
a+b=163
So,
(63,100),(65,63),....(99,64)
Total 19 pairs.
No further case possible.
So, required number is
=12+35+42+19=108