Let us convert the percentages to decimal format first.. so 5% is just 5/100 or 0.05 and 15% is just 15/100 or 0.15
so hmmm, so, let's say it needs "x" amount and "y" amount of each respectively, so, whatever "x" and "y" are, they must add up to 100, and whatever their concentration is, must add up to what the mixture yields
Grandpa's age is 75 years Seven times the age of junior = age of grandpa + 9 jears = 75 + 9 = 84 years Hence, the age of junior will be 84 / 7 = 12 years. (Since 84 is seven times his age, you have to devide by seven). --> Junior is 12 years old.