Question

Find the units' digit in the expression $(515{)}^{31}+(525{)}^{90}$ ?

Answer 1

Since the units' digit of any number written as a power of 5 is always 5
Units' digit in the expression $(515{)}^{31}+(525{)}^{90}$
$=$ Units' digit of $5^{31}$+ Units digit of $5^{90}$
$=$ Units' digit of $(5+5)=10=0$