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harsh.champ
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Find the digit at the ten's place of the number N = 7281 * 3264.
(A)3
(B)4
(C)5
(D)6
(E)7
The OA is D.
Don't look at the soln. before you solve it yourself.
[spoiler]In other words the question asks to find out the remainder
when the expression is divided by 100 and then take the left
most digit as the final result.
Also, 720k when divided by 100 gives remainder 1.
(Here K is a positive integer)
720k = (49)10k = (50 - 1)10k.
In the expansion of (50 - 1)10k, every term except the last term,
i.e. 1 will be divisible by 100.
Therefore, when 720k is divided by 100, the remainder is 1.
Even, 320K when divided by 100 gives remainder 1.
So, 7281 × 3264 by 100 ⇒ 7 × 34 by 100 ⇒ 67 by 100.
Hence, the digit at the tens place is 6.[/spoiler]
(A)3
(B)4
(C)5
(D)6
(E)7
The OA is D.
Don't look at the soln. before you solve it yourself.
[spoiler]In other words the question asks to find out the remainder
when the expression is divided by 100 and then take the left
most digit as the final result.
Also, 720k when divided by 100 gives remainder 1.
(Here K is a positive integer)
720k = (49)10k = (50 - 1)10k.
In the expansion of (50 - 1)10k, every term except the last term,
i.e. 1 will be divisible by 100.
Therefore, when 720k is divided by 100, the remainder is 1.
Even, 320K when divided by 100 gives remainder 1.
So, 7281 × 3264 by 100 ⇒ 7 × 34 by 100 ⇒ 67 by 100.
Hence, the digit at the tens place is 6.[/spoiler]
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