wiz-icon
MyQuestionIcon
MyQuestionIcon
7
You visited us 7 times! Enjoying our articles? Unlock Full Access!
Question

If j, k, and n are consecutive integers such that 0<j<k<n and the units (ones) digit of the product jn is 9, what is the units digit of k ?

A
0
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
B
1
No worries! We‘ve got your back. Try BYJU‘S free classes today!
C
2
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
3
No worries! We‘ve got your back. Try BYJU‘S free classes today!
E
4
No worries! We‘ve got your back. Try BYJU‘S free classes today!
Open in App
Solution

The correct option is A 0

There are only a few ways you can make a product have a units digit of 9. Either both numbers you’re multiplying have to be 3, or one has to be 1 and one has to be 9. Since we’re dealing with consecutive integers, j and n can’t both end in 3, so they’re going to have to end in 1 and 9.

It’s important to remember that although we only really care about the units digits in this problem, we’re dealing with numbers that might (or in fact, must) be 2 or more digits. That’s why you can have ks units digit be 0.

Say j=19, k=20, and n=21. Then jn=(19)(21)=399 (units digit is 9), and the units digit of k=0.

Hence option A is correct.


flag
Suggest Corrections
thumbs-up
0
Join BYJU'S Learning Program
similar_icon
Related Videos
thumbnail
lock
Introduction
MATHEMATICS
Watch in App
Join BYJU'S Learning Program
CrossIcon