BDMO National Primary 2018/6

Discussion on Bangladesh Mathematical Olympiad (BdMO) National
User avatar
nahin munkar
Posts:81
Joined:Mon Aug 17, 2015 6:51 pm
Location:banasree,dhaka
BDMO National Primary 2018/6

Unread post by nahin munkar » Tue Jan 08, 2019 1:32 pm

An even number is called a ‘good’ even number if its first and last digits are also an even number. How many $3$-digit ‘good’ even numbers are there? Try to find their number without writing all such number!
# Mathematicians stand on each other's shoulders. ~ Carl Friedrich Gauss

samiul_samin
Posts:1007
Joined:Sat Dec 09, 2017 1:32 pm

Re: BDMO National Primary 2018/6

Unread post by samiul_samin » Thu Jan 10, 2019 12:59 am

For the first digit there are $4$ options ($2,4,6,8$).
For the middle digit there are $10$ options($0,1,2,3,4,5,6,7,8,9$).
For the last digit there are $5$ options($0,2,4,6,8$)
So there are total $4×10×5$ or $200$ such even numbers.

Post Reply