1100 boys and 900 girls appeared in an examination. Out of them 50% boys and 40% girls passed the examination. Accordingly the percentage of failed candidates is how much was it?

Given: 1100 boys and 900 girls appeared in an examination. Out of them 50% boys and 40% girls passed the examination.

Total Candidates:

1100 + 900 = 2000

Pass Candidates:

Boys Passed:

​$$\frac {50}{100}$$ $$\times$$ 1100 = 550

Girls Passed:

​$$\frac {40}{100}$$ $$\times$$ 900 = 360

Total Passed:

550 + 360 = 910

Failed Candidates: 

2000 - 920 = 1090

Percentage of failed candidates:

​$$\frac {1090}{2000}$$ $$\times$$ 100 = 54.5%

54.5% failed candidates.

Thus, correct option is (b).