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Question

A boy multiplies 987 by a certain number and obtained 559981 as his answer. If in the answer both 9 are wrong , but the other digits are correct, then what will be the correct answer?
Options:
A .  556581
B .  555681
C .  555181
D .  553681
Answer: Option B

Answer : Option B

Explanation :

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Solution 1
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The answer is divisible by 987.
So we can use hit and trial method to find out the number divisible by 987
from the given choices
553681 ÷ 987 gives a remainder not equal to 0
555181 ÷ 987 gives a remainder not equal to 0
556581 ÷ 987 gives a remainder not equal to 0
But 555681 ÷ 987 gives 0 as remainder. Hence this is the answer
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Solution 2 (Recommended)
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The answer is divisible by 987.
If a number is divisible by two co-prime numbers, then the number is divisible by their
product also.
If a number is divisible by more than two pairwise co-prime numbers,
then the number is divisible by their product also.
before proceeding
further.
556581 is divisible by 3
556581 is not divisible by 7
Hence 556581 is not divisible by 987
555181 is not divisible by 3
Hence 555181 is not divisible by 987
553681 is not divisible by 3
Hence 553681 is not divisible by 987
555681 is divisible by 3
555681 is divisible by 7
555681 is divisible by 47
Hence 555681 is divisible by 987 also


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