What denominator for 21/3=49/ ?

To find the denominator that would make the ratios ( \frac{21}{3} ) and ( \frac{49}{x} ) proportional, we can set up the equation:

[ \frac{21}{3} = \frac{49}{x} ]

First, we can simplify ( \frac{21}{3} ):

[ \frac{21}{3} = 7 ]

Now we have:

[ 7 = \frac{49}{x} ]

Next, we can cross-multiply to solve for ( x ):

[ 7x = 49 ]

Now, divide both sides by 7:

[ x = \frac{49}{7} = 7 ]

Therefore, the denominator that would make the ratios proportional is ( 7 ).