Wow! Here you have 3 fractions with 3 different denominators that have nothing in common. In cases such as this one you find the LCD by mult. all of the given denominators together. Thus, in this case, your LCD is 4(5)(3) = 60.
To find the least common denominator of the three fractions, list out the multiples of each denominator:
Multiples of 3: {3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60} Multiples of 4: {4,8,12,16,20,24,28,32,36,40,44,50,55,60} Multiples of 5: {5,10,15,20,25,30,35,40,45,50,55,60}
The least common denominator of these three fractions is 60.
Let's assign the speed of Jerry in still air as <em>x </em> (in km/h)
Let's assign the speed of the wind as <em>y </em>(in km/h)
With the wind as Jerry’s back, he takes 10 minutes to get to the library. We can create the following equation. (<em>we are converting the minutes to hours by dividing by 60</em>);
2.5 / (x + y) = 10/60
10x + 10y = 150
x + y = 15
With the wind against Jerry, he takes 15 minutes from the library. We can create the following equation;
2.5 / (x-y) = 15/60
15x – 15y = 150
x – y = 10
We can now solve the simultaneous equation by subtraction;
