EM-1632

Writing algebraic expressions

E Math · Secondary 4 · Hard · Writing algebraic expressions

A number has tens digit

a

and units digit

b

. The number is between 10 and 99. The digits are added and the sum is subtracted from the original number. Show that the result is always a multiple of 9.

$9a$ , which is always a multiple of 9
$a+b$ , which is always a multiple of 9
$9b$ , which is always a multiple of 9
$10a-b$ , which is always a multiple of 9

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