Cannn you please tell me the answer of 28,29 and 30 with proper explanation

 

Dear student,
Here is the solution of your asked query:
$$\begin{gathered} 28. \mathrm{Since} \mathrm{the} \mathrm{number} \mathrm{of} \mathrm{red}, \mathrm{blue} \mathrm{and} \mathrm{green} \mathrm{marbles} \mathrm{are} \mathrm{in} \mathrm{the} \mathrm{ratio} 5:3:7. \\ \mathrm{So} \mathrm{let} \mathrm{number} \mathrm{of} \mathrm{red}, \mathrm{blue} \mathrm{and} \mathrm{green} \mathrm{marbles} \mathrm{be} 5\mathrm{x}, 3\mathrm{x} \mathrm{and} 7\mathrm{x} \mathrm{respectively}. \\ \mathrm{And} \mathrm{it} \mathrm{is} \mathrm{given} \mathrm{that} \mathrm{number} \mathrm{of} \mathrm{green} \mathrm{marbles} = 42 \\ \mathrm{so}, 7\mathrm{x}=42 \\ \Rightarrow \mathrm{x}=\frac{42}{7}=6 \\ \mathrm{Therefore} \mathrm{total} \mathrm{number} \mathrm{of} \mathrm{marbles} = 5\mathrm{x}+3\mathrm{x}+7\mathrm{x}=15\mathrm{x} = 15\times 6=90 \\ 29. \mathrm{Since} \mathrm{three} \mathrm{portions} \mathrm{are} \mathrm{in} \mathrm{the} \mathrm{ratio} 2:5:7. \\ \mathrm{so} \mathrm{let} \mathrm{the} \mathrm{portions} \mathrm{be} 2\mathrm{x}, 5\mathrm{x} \mathrm{and} 7\mathrm{x} \\ \mathrm{Here} \mathrm{smallest} \mathrm{portion} \mathrm{is} 2\mathrm{x}. \\ \mathrm{so}, 2\mathrm{x}=40\mathrm{kg} (\mathrm{as} \mathrm{given}) \\ \Rightarrow \mathrm{x}=\frac{40}{2}=20 \\ \mathrm{And} \mathrm{heaviest} \mathrm{portion} \mathrm{is} 7\mathrm{x}. \\ \mathrm{So} \mathrm{weight} \mathrm{of} \mathrm{largest} \mathrm{portion} =7\times 20=140 \mathrm{kg} \\ \mathrm{So} \mathrm{difference} \mathrm{between} \mathrm{the} \mathrm{weight} \mathrm{of} \mathrm{largest} \mathrm{and} \mathrm{smallest} \mathrm{portion} = 140\mathrm{kg}-40\mathrm{kg} =100\mathrm{kg} \\ \mathrm{Therefore}, \mathrm{largest} \mathrm{portion} \mathrm{is} 100 \mathrm{kg} \mathrm{heavier} \mathrm{than} \mathrm{smallest} \mathrm{portion}. \end{gathered}$$
For remaining query, we request you to post them in separate threads.

Regards