Answer:
5 students are left out in the arrangement.
Step-by-step explanation:
If the number of rows = the number of columns
Then there must be an equal arrangement
Since the total number of students in the school is 2121
Then, the students that are left out in this arrangement = 2121 - (√2121 X √2121
Note the result of the square root would only consider the whole number, the digits after the decimal point signifies the remaining number that can't fit into the arrangement
so, √2121 = 46.05 (so 46 would be used)
= 2121 - (46 X 46)
= 2121 - 2116 = 5
Therefore 5 students are left out in the arrangement.
Ok. In order to do this set up 2/5 divided by 5/7. The way you divide with fractions is by multiplying them but flipping the second fraction into 7/5 <---this is known as the reciprocal. In other words do:
2/5 x 7/5 =
14/25
There you go.
ANSWER: 32 five-dollar bills
======
EXPLANATION:
Let x be number of $5 bills
Let y be number of $10 bills
Since we have total of 38 bills, we must have the sum of x and y be 38
x + y = 38 (I)
Since the total amount deposited is $220, we must have the sum of 5x and 10y be 220 (x and y are just the "number of" their respective bills, so we multiply them by their value to get the total value):
5x + 10y = 220 (II)
System of equations:

Divide both sides of equation (II) by 5 so our numbers become smaller

Rearrange (I) to solve for y so that we can substitute into (II)

Substituting this into equation (II) for the y:

We have 32 five-dollar bills
======
If we want to finish off the question, use y = 38 - x to figure out number of $10 bills

32 five-dollar bills and 6 ten-dollar bills
The answer is 35/10 and 6/10
One answer (of several) would be 33: It's between 10 and 200 and the sum of its digits is 6. Continue this same pattern to identify other answers.