Does S B Women's College, Department of Library & Information Science provide 100% placement?

To get admission to the BA programme at Ranchi Women's College, you need to apply online through the Chancellor's Portal and your admission will be based on merit, determined by your performance in the +2 (intermediate) examination. Ensure you meet the eligibility criteria, which includes a minimum of 45% marks in the relevant subjects at the +2 level. 

Yes, BCA is a technical degree and it's better if you have prior knowledge of clss 12th maths but it's not totally compulsory to have maths in your prior classes. You can manage it by extra classes or tutions.

Whether you can get admission to a Women's College with fifty-five percent depends heavily on a few factors. Firstly, which specific "Women's College" are you referring to? Highly selective colleges in major cities might have higher cut-offs, especially for popular courses. Secondly, the course you're interested in plays a role – humanities courses might have lower requirements than Science or commerce. Your best bet is to check the official prospectus or website of the specific college for their minimum eligibility criteria and previous year's cut-off percentages for your desired program.

From the search result, I could not determine the number of students that would be admitted in the M. Lib. I. Sc course at S B Women's College, Department of Library & Information Science. Such courses usually accommodate very limited numbers of students as dictated by faculty and institutional capacity.
A college like S B Women's College in general usually will take about 30-50 students for a postgraduate course; that could vary some time, do check in the college or on the website as well for exact seats of the M. Lib. I. Sc course.