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I dunno if this might be correct...
consider first four powers of 7...
71=7
72=49
73=343
74=2401...
after this,the series of last digits goes on repeating..
Now,for 7x+7y,x can be chosen in 4 ways (from the 1st 4 no.s),y can be chosen in 4 ways(from 1st 4 no.s)...
so,total pairs of (x,y) is 16...but acc. to condn.,only(1,3) and (2,4) satisfy it...
so prob.=fav. cases/total cases=2/16=1/8...
I havent considered the rest of no.s coz the series keeps on repeating...so i think the prob. will still remain same...
Am i correct??
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Moderation Team
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