Which pairs of ratios could be used to form a proportion?
a) 3/3, 7/7
b) 1/3, 3/5
c) 4/3, 3/4
d) 6/1000 , 12,1000

 The correct answer is:  

                           →    [A]:  " 3/3,  7/7 "  ;

→   since each ratio in this pair is equal to each other;  that is:

    " 3/3 = 7/7 " ;  

→  Note:  " 3/3 = (3÷3) / (3÷3) = 1 / 1 = 1 " ;  

          or:  " 3/3 = 3 ÷ 3 = 1 " ;

 →  And: " 7/7 = (7÷7) / (7÷7) = 1 / 1 = 1 " ;  

          or:  " 7/7 = 7 ÷ 7 = 1 " ;

Thus:  " 3/3 = 7/7 = 1/1 = 1 " .

Let us consider the other answer choices:

Choice [B]:  " 1/3, 3/5 " ;  is incorrect;  since:  " (1/3) ≠ (3/5)" .

 Note:  "(1/3) = 0.3333 )"  ;  and:   "(3/5) = 0.6 " .

    0.3333...  ≠  0.6 .

Choice [C]:  " 4/3, 3/4 ", is incorrect; since:  " (4/3) ≠ (3/4) " .

 Note:  "(4/3) = 1.33333 ...) " ;  and:  "(3/4) = 0.75 ".

    1.3333 ≠ 0.75 .

Choice [D]:  " 6/1000,  12/1000 " ;  is incorrect ;

   since:  "6/1000 ≠ 12/1000 " ;  And:

    since:  "6" out of 1000" is less than:  "12" out of "1000" ;

    → Specifically:   0.006 ≠  0.012 .        

answer: 7

step-by-step explanation: