Question

the product of two digit numbers is 1938 if the product of their unit digit is 28 and that of tens digit is 15 find the numbers

Answer 1

the unit's digits multiply to 28 and 28 can be the product of 2 1-digit numbers in only 1 way that is 28=7*4 so the unit digits are 7 and 4 

now the tens digits mutiply to 15, this also can only be the product of 2 1-digit numbers in only 1 way and that is 15=5*3 so the ten's digits are 5 and 3. 

So the 2 numbers are either 57 and 34, or 54 and 37. Multiplying these togeather we get 
57*34=1938 
54*37=1998 

So 57 and 34 must be the 2 numbers