Let x be the number of girls at the beach. The ratio of boys to girls at the beach cleanup was 7 : 8. If there were 42 boys and x girls, you can write a proportion:
[tex]\dfrac{42}{x}=\dfrac{7}{8}.[/tex]
Use the main property of proportion:
[tex]42\cdot 8=7\cdot x,\\ \\x=\dfrac{42\cdot 8}{7},\\ \\x=6\cdot 8=48.[/tex]
Answer: 48 girls
