A Tricky Problem or Not?

Algebra Level 1

What is the unit digit of the following number?

21 × 23 × 25 × 27 × 29 × 31 × 33 × 35 × 37 × 39 − 2015 21\times23\times25\times27\times29\times31\times33\times35\times37\times39-2015


The answer is 0.

Victor Paes Plinio by Victor Paes Plinio , 21, Brazil

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2 solutions

Mohit Gupta
Jun 3, 2015

Its easy when you see the unit digits of no.Being multiplied you will see all are odd. Therefore unit digit of multiplying no.=5×odd and at last 5-5=0

2 Helpful 0 Interesting 0 Brilliant 0 Confused
Ramiel To-ong
Jun 8, 2015

zero since the last digit for all the product is 5 subtracted by the last digit of 2015 which is 5 then the last digit will always be 5

0 Helpful 0 Interesting 0 Brilliant 0 Confused

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