Answer:
Step-by-step explanation:
3×8-2×3=18
I believe it is the first one but I might be wrong.
There are 80 children. 45 of them are girls. The amount of boys is equal to:

That means there are 45 girls and 35 boys.
The ratio of boys to girls is: 
Simplify:

Your answer is 7:9
There are many ways to solve number 5 as it is just an reduce/enlargement of equidistant fractions
The first method that came up to my mind is just dividing denominators.
For A) you can do 72 divided by 18 which would give you 4. Then you can divide the given numerator with the answer you got from dividing the denominators. This would be 8 divided by 4 which would give you two. This means that 2/18 is equal to 8/72. You can check by simplifying the fraction. Both 2/18 and 8/72 equal 9 when simplified, therefore correct.
You can use this method for b, either use a calculator because of the decimals or just remove the decimals and replace them later. Make sure when you use this method, you are always dividing the bigger number. So in B you would do 40.3 divided by 12.4
Answer: This is what I could figure out
Step-by-step explanation: