[tex]a) \frac{15}{100} \times x = 225[/tex]
[tex] \frac{3}{20} \times x = 225[/tex]
[tex] \frac{3x}{20} = 225[/tex]
[tex]3x = 225 \times 20[/tex]
[tex]3x = 4500[/tex]
[tex]x = \frac{4500}{3} [/tex]
[tex]x = 1500[/tex]
[tex]b) \frac{40}{100} \times x = 640[/tex]
[tex] \frac{4}{10} \times x = 640[/tex]
[tex] \frac{2}{5} \times x = 640[/tex]
[tex] \frac{2x}{5} = 640[/tex]
[tex]2x = 5 \times 640[/tex]
[tex]2x = 3200[/tex]
[tex]x = \frac{3200}{2} [/tex]
[tex]x = 1600[/tex]
[tex]c) \frac{75}{100} \times x = 1872[/tex]
[tex] \frac{3}{4} \times x = 1872[/tex]
[tex] \frac{3x}{4} = 1872[/tex]
[tex]3x = 1872 \times 4[/tex]
[tex]3x = 7488[/tex]
[tex]x = \frac{7488}{3} [/tex]
[tex]x = 2496[/tex]
