how many positive integers less than 1960 are such that the product of their digits is 10.
Pick:
A) 220 B) 230 C) 280 D) 220 E) 240
1960 is divisible by 10 ( or 2*5) = 196   196 is divisible by 4 = &gt; 49   49 = 7 *7   hence 1960 is divisible by 2,4,5, 7 ,7   if there were only one 7,   i.e if the problem were 280   280
<result>C</result>
how many positive integers less than 1960 are such that the product of their digits is 10.