Yes there is actually a formula for this. This is an arithmetic progression with a common difference of 1.
The sum of terms can be solved by using the formula
S = (n/2) * (a1 + an)
where S is the sum of the terms
n is the number of terms
a1 is the first term
an is the last term
we can calculate the number of terms, n by using the formula
an = a1 + (n-1)*d
d is the common difference equal to 1
therefore n = 51
substituting to the first equation
S = 2805
Answer:
Option 'b' i.e. -11/20 is the correct option.
Thus,

Step-by-step explanation:
Given the expression

Determining the difference of the fractions

The Least Common Multiplier of 5, 4 is 20. Thus, adjust the fractions based on the L.C.M.

Apply the fraction rule: 

Add the number: 4-15 = -11

Apply the fraction rule: 

Please check the attached figure, where the pointing-down arrow is representing the correct answer which is -11/20.
Therefore, option 'b' i.e. -11/20 is the correct option.
Thus,

Answer:
5*4*3*2*1= 120
you multiply each number to it's previous one till you reach 1
Answer: length = 8 units
Width = 2 units
Step-by-step explanation:
Let the length of the rectangle be represented by L
Let the width of the rectangle be represented by W
The sum of 5 times the width of a rectangle and twice its length is 26 units. This means that
5W + 2L = 26 - - - - - - - - 1
The difference of 15 times the width and three times the length is 6 units. It means that
15W - 3L = 6 - - - - - - - - 2
The system equations are equation 1 and equation 2.
Multiplying equation 1 by 3 and equation 2 by 2, it becomes
15W + 6L = 78
30W - 6L = 12
Adding both equations,
45W = 90
W = 90/45 = 2
15W - 3L = 6
15×2 - 3L = 6
-3L = 6 - 30 = - 24
L = - 24/ -3 = 8