Which of the following numbers has the largest number of unique prime factors?: {78, 217, 74, 420}

1 Answer
Apr 30, 2016

#420# has the largest number of unique prime factors.

Explanation:

Prime factors of #78# are #2#, #3# and #13# as #78=2xx3xx13#

Prime factors of #217# are #7# and #31# as #217=7xx31#

Prime factors of #74# are #2# and #37# as #74=2xx37#

Prime factors of #420# are #2#, #3#, #5# and #7# as #420=2xx2xx3xx5xx7#

Hence, #420# has the largest number of unique prime factors.