68.
In a mathematics class Raju was requested to add square of first 10 natural numbers and Rani was
requested to add cubes of first 10 natural numbers. After the calculation made by Raju and Rani, Ravi was
requested to find the sum of the values obtained by Raju and Rani, Rahim was asked to subtract the sum
obtained by Rani from the sum obtained by Raju. Finally Roshan was requested to calculate the sum ofthe
values obtained by Ravi and Rahim. Then what was the sum obtained by Roshan?
A) 550
B) 660
C) 770
D) 880
Answers
Answer:
C)770
explanation
Raju :sum of the squares of the first 10 natural numbers = 10(10+1)(20+1)/6=
385
Rani :sum of the cubes of first 10 natural numbers =(10(10+1))²÷4
3025
Ravi:add values obtained by Rani and Raju =3025+385=3410
Rahim :subtract values obtained by Rani from raju =385-3025=-2640
Roshan :add the values obtained by Rahim and Ravi= -2640+3410 =770
Given : Raju was requested to add the square of the first 10 natural numbers and Rani was requested to add cubes of the first 10 natural numbers.
To Find : sum obtained by Roshan
A) 550
B) 660
C) 770
D) 880
Solution:
Raju was requested to add the square of the first 10 natural numbers
∑n² = n(n+1)(2n+1)/6 = 10 (11)(21)/6 = 385
Raju = 385
Rani was requested to add cubes of the first 10 natural numbers.
∑n³ = {n(n+1)/2}² = {10 (11)(2)}² = 55² = 3025
Rani = 3025
Ravi was requested to find the sum of the values obtained by Raju and Rani,
Ravi = 385 + 3025 = 3410
Ravi = 3410
Rahim was asked to subtract the sum obtained by Rani from the sum obtained by Raju.
Rahim = 385 - 3025 = -2640
Roshan was requested to calculate the sum of the values obtained by Ravi and Rahim
sum obtained by Roshan = 3410 - 2640 = 770
sum obtained by Roshan = 770
option C is correct
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