A 1:13 ratio means that there is one pair tree for every 13 apple trees.
In order to find out how many apple trees there are out of 42 total trees, we need to find the percentage of the total trees that are apple trees. We can find out the percentage from the ratio that we were given.
A 1:13 ratio will mean 1 out of every 14 trees is a pair tree and 13 out of every 14 trees is an apple tree. To find the percentage of the whole population that is apple trees divide 13 by 14.
Multiply 0.92857 by 42 total trees to find the number of apple trees you have in the whole population:
Therefore, you have 39 apple trees in your group of 42 trees.