================================================
Explanation:
We'll step through the grade levels in increasing order
The teacher starts with 700 sour worms total. Then 2/7 of that is given to the Kindergartners
2/7 of 700 = (2/7)*700 = 200
So Ms. Mitchell handed out 200 worms to the Kindergartners.
This means she has 700-200 = 500 left over.
-----------------
Now onto the 1st graders.
The teacher hands out 7/25 of the remaining total (500) to the first graders
7/25 of 500 = (7/25)*500 = 140
She hands out 140 worms to the first graders and has 500-140 = 360 worms left.
-------------------
Now the 2nd graders
"Of the remaining worms, she gives 4/9 to the 2nd graders" tells us that
4/9 of 360 = (4/9)*360 = 160 worms are given to the second graders
This leaves 360-160 = 200 worms left
-------------------
Now the 3rd graders
37/50 of 200 = (37/50)*200 = 148
The teacher hands out 148 worms to the 3rd graders
There are 200 - 148 = 52 worms left.
--------------------
Finally, we're at the 4th graders
Each 4th grader gets the same number of worms (aka the amount is distributed equally). Since there are 52 worms left, and 13 fourth graders, this means each fourth grader gets 52/13 = 4 worms. It's a slightly interesting coincidence that the number '4' matches up with the grade level. It's possible your teacher adjusted the numbers to make this an intentional goal.
--------------------
To recap everything, we found these worm counts for each grade level
Note how those values add back up to 700, ie 200+140+160+148+52 = 700. This helps confirm the answer.
Then once we see that 52 worms are left, each fourth grader gets 52/13 = 4 worms a piece.
So this is why the final answer is 4.
