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How many numbers are there between 101 and 999, which are divisible by both 2 and 5?

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The numbers which are divisible by both 2 and 5 are divisible by 10 also.  
Now, the numbers between 101 and 999 which are divisible 10 are 110,120,130,..,990.  
Clearly, these number are in AP Here, a=110 and d=120−110=10  
Let this AP contains n terms. Then,
a n ​ =990
⇒110+(n−1)×10=990
⇒10n+100=990
⇒10n=990−100=890
⇒n=89
Hence, there are 89 numbers between 101 and 999 which are divisible by both 2 and 5.
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