what are all the different ways to choose the tens digit, a, and the ones digit, b, in the number 631872ab so that the number will be divisible by 9? explain your reasoning

Respuesta :

The number of different ways to choose the ten digit number is divisible by 9 is  11 ways  .

In the question ,

it is given that ,  

the number is 631872ab ;

and also the number is divisible by 9 ,

we know that the number is divisible by 9 , then the sum of digits is also divisible by 9 .

the sum of the digits is = 27 + a + b .

for 27 + a + b to be divisible by 9 , a+b should be divisible by 9 .

So , we can choose a+b = 0  or a+b = 9  .

for a+b = 0  , the ordered pair is (0,0) that is 1 way

for a+b = 9 , the ordered pair for (a,b) is (0,9) , (1,8) , (2,7) , (3,6) , (4,5) , (5,4) , (6,3) , (7,2) , (8,1) and (9,0) that is 10 ways .

So , the total number of possible pairs is 1 + 10 = 11 ways .

Therefore , the number of different ways of selection is 11 ways .

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