Question

There were ships with 3 masts and ships with 4 masts at the Tall ship exhibition. Mollie counted a total of 30 masts on 8 ships she saw. How many of these ships had 4 masts?

Answer 1

We will use x and y variables to help calculate the number of ships

x = variable for amount of ships with 4 masts
y = variable for amount of ships with 3 masts


Mollie saw a total of 30 masts on 8 ships.
Based on this, we can conclude that:

• x + y = 8 (x amount of 4 mast ships + y amount of 3 mast ships)

• 4x + 3y = 30 (the amount of masts she saw)


From these 2 equasions we can calculate the amount of ships. We will use the first equasion and put x on the right side of the equasion so we get the approximate value of y:
$x + y = 8 \\ y = 8 - x$

Now we insert (8 -x) into our second equasion in the place of y and calculate it:
$4x + 3(8 - x) = 30 \\ 4x + 24 - 3x = 30 \\ 4x - 3x = 30 - 24 \\ x = 6$
RESULT: There were 6 ships with 4 masts