Answer:
12
Step-by-step explanation:
Let's create a table
![\left[\begin{array}{cc}boys&girls\\2&5\\2x&5x\end{array}\right]](https://tex.z-dn.net/?f=%5Cleft%5B%5Cbegin%7Barray%7D%7Bcc%7Dboys%26girls%5C%5C2%265%5C%5C2x%265x%5Cend%7Barray%7D%5Cright%5D)
2 : 5 is the same as 2x : 5x because you multiply both sides in 2:5 by x
If the ratio is 2x : 5x, what is the total?
2x + 5x = 7x
The total is 7x
However, we are given that there are 42 students
So, 7x = 42
x = 6
As we said earlier, boys = 2x
We know that x = 6, so 2x must equal to 12
There are 12 boys.
Hope this helps :)
Have a nice day!