Explain how knowing 1+7 you find the sum for 7+1

Ijust need to see how to do this. so you don’t have to answer all of them just a step by step explanation of one.

In priyas math class there are 10 boys and 15 girls. what is the ratio of boys to girls in priyas math class? express your answer as a decimal

For the chance to be team captain, the numbers 1-30 are put in a hat and you get two chances to pick a number, without replacement. which formula correctly shows how to find the probability that you choose the number 1 and then 2?