CAT 2013 Exam

51588 Followers - 339 Articles - 2077 Questions and Answers

Learn By Example

by Suresh

In this lesson I am going to discuss a concepts straight away by solving a question rather than discussing the whole new concept.

How many digits cannot be the unit's digit of the product of three 3-digit numbers whose sum is 989

When we read the problem, it looks like what the hell is it asking? But, it is not that difficult a problem if we go by a method

let the three 3 digit numbers be xyz, abc and pqr

then what the question essentially says is z+c+r=9 or 19

now we have to check if d is the last digit of the product of xyz, abc and pqr, then what are the values d cannot take.

it can be easily checked that it works for 0 and 2 so d can be o or 2

for d=1, (z,c,r)=(9,3,3) or(9,9,1) and others

9+9+1=19 satisfies hence d can be 1

d=3, (z,c,r)=(3,1,1),(3,7,3),(9,7,1) but none of which sum to 9 or 19

hence d cant be 3

d=4 (1,1,4) (1,2,2) (7*3*4),(4*4*4),(8*8*1)(9*8*2) and others

d=4 works

d=5 is obvious (5*1*3)

d=6 is (1*1*6),(1*2*3) (4*4*1)

which works

hence d=6 works too

d=7 works for 7*1*1

d=8 (4*2*1) (6*8*1) (6*2*4)(2*2*2) (2*3*8)

d=8 does not work

d=9 will work for (9*7*3)

so d=3,8 does not work

Hence 2 digits cant be unit digits !

1 Comment
    Current Rating
    Rate Up
    Rate Down
    sakaThu, 15 Jan 2009 12:12:13 -0000

    where is concept its straight equation solving..or numeric….

    Post Comments

    Reply to This

Your Comment

Current Rating
Rate Up
Rate Down
Have an account? Log In

Textile is Enabled. View Reference.

Think Beyond CAT Apply to Top MBA Colleges in the World

Fill out your information accurately in this form to learn more about the world's Best MBA programs.

About the Author

About: Worked for more than 6 years in renowned corporate institutes as their core faculty/lead content developer for C.A.T,G.R.E, G.M.A.T and Campus Recruitment Training Programs.

Last Updated At Dec 07, 2012

1 Comment

Similar Articles

More Lessons