A student finds the sum 1 + 2 + 3 + ... as his patience runs out. He found the sum as 575. When the teacher declared the result wrong, the student realized that he missed a number. What was the number the student missed? Choose the correct choice from the following
A) 16	B) 18	C) 14	D) 20	E) 22
Explanation :   Sum of 1st 10 natural numbers (1 – 10) = 1 + 2 + …10 = 55.   Sum of next 10 natural numbers (11 – 20) = 10 + 11 + 12 +…20 = 100 + 55= 
<gadget id="calculator">100 + 55</gadget>
<output>155</output>
155.   Sum of next 10 natural numbers (31 – 40)= 255.   Sum of numbers from 31 – 40 = 355 and so on and on.   So, we have here   55 + 155 + 255= 
<gadget id="calculator">  55 + 155 + 255</gadget>
<output>465</output>
465.   If we add 355 to 465, it will be way more than 575.   So, we can add one by one.   465 + 31 + 32 + 33= 
<gadget id="calculator">465 + 31 + 32 + 33</gadget>
<output>561</output>
561.   465 + 31 + 32 + 33 +34= 
<gadget id="calculator">465 + 31 + 32 + 33 +34</gadget>
<output>595</output>
595.   Thus, the sum should be 595 instead of 575, and the missing number is 20.   Answer : 20
<result>D</result>
A student finds the sum 1 + 2 + 3 + ... as his patience runs out. He found the sum as 575. When the teacher declared the result wrong, the student realized that he missed a number. What was the number the student missed?