Question

Question 70 (iv)

Work out the following multiplication.

$12345679\ast 9\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

Use the result to answer the following question.

By what number should 12345679 be multiplied to get 999999999?

Answer 1

We have, $12345679\ast 9\_\_\_\_\_\_\_111111111$
Here, we observe that in the product all the digits are same i.e. 1, which is actually the unit digit of the product $9\times 9$, Also, the total of digits in the multiplier is 9.
To get the number 9 in the product we have to find out a two-digit number whose sum of digits is 9 and the product of its unit's digit with the unit's digit of the given number is 9, such number is 81.