The First by the First and the Last by the Last
112 + 222 + 332 + 442 + 552 = ?
a) 4505
b) 5566
c) 5808
d) 6655
e) 7105
This question was given in the Juniors and older age groups in the 1st Math2Shine International Vedic Mathematics Competition which was held last July 22, 2023.
A variation of this question, 222 + 332 + 442 = ?, was also given in the Beginners and Primary categories.
This is a very easy question, but it would involve lengthy calculations using the traditional methods.
Most people would square all 5 numbers and then add the squares:
112 = 121
222 = 484
332 = 1089
442 = 1936
552 = 3025
121 + 484 + 1089 + 1936 + 3025 = 6655
Many would find that computing 112 + 222 + 442 first would save time, since the expression can be converted to 112 +(2 x 11)2 + (4 x 11)2 or (1 + 4 + 16) x 112 which reduces to a simple (21 x 121= 2541) multiplication.
In the Beginners and Primary version of the question, getting the value of 222 + 442 is easier. (2 x 11)2 + (4 x 11)2 = 20 x 121 = 2420.
The Vedic Math solution of applying the Sutra, the First by the First and the Last by the Last, would not give us the exact answers to the problems but would give us the best among the choices offered.
We begin by squaring the last digits of the numbers (the Last by the Last) and adding as we go along:
12 + 22 = 1 + 4 = 5
5 + 32 = 14
14 + 42 = 30
And 30 + 52 = 55.
Therefore, the answer must end in 5 and we can eliminate b) 5566 and c) 5808. We can also eliminate choice a) 4505 because the first two digits of the answer must be greater than 55.
We are thus, left with two choices d) 6655 and e) 7025.
The next step is to estimate the value of 152 + 252 + 352 + 452 + 552 because the value we get here is very much more than the answer to our problem. Applying “by one more than the one before” to the first digits of the numbers to be squared (the First by the First) and adding them as we go along, we have:
1 x 2 = 2
2 + (2 x 3) = 8
8 + (3 x 4) =20
20 + (4 x 5) = 40
40 + (5 x 6) = 70
We cannot have e) 7025 as the answer. So, what remains is d) 6655.
Can you apply this method in solving the version for the Beginners and Primary group?
