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If 21y5 is a Multiple of 9, Where Y is a Digit, What is the Value of Y? - CBSE Class 8 - Mathematics

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Question

If 21y5 is a multiple of 9, where y is a digit, what is the value of y?

Solution

If a number is a multiple of 9, then the sum of its digits will be divisible by 9.

Sum of digits of 21y5 = 2 + 1 + y + 5 = 8 + y

Hence, 8 + y should be a multiple of 9.

This is possible when 8 + y is any one of these numbers 0, 9, 18, 27, and so on …

However, since y is a single digit number, this sum can be 9 only. Therefore, y should be 1 only.

  Is there an error in this question or solution?

APPEARS IN

 NCERT Solution for Mathematics Textbook for Class 8 (2018 to Current)
Chapter 16: Playing with Numbers
Ex. 16.20 | Q: 1 | Page no. 260
Solution If 21y5 is a Multiple of 9, Where Y is a Digit, What is the Value of Y? Concept: Tests of Divisibility - Divisibility by 9 and 3.
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