Respuesta :

Luv2Teach
Set this up as a proportion with cement on top and sand on bottom.  Our proportions will look like this then: [tex] \frac{1}{3} = \frac{7}{x} [/tex].  Cross multiply to get x = 21.  So 21 shovels of sand is needed.
frika
Let x be the amount of cement and y be the amount of sand. If the ratio of cement to sand for mortar is 1:3, then [tex] \frac{x}{y} = \frac{1}{3} [/tex] and y=3x.

So, if Sandy puts in x=7 shovels of cement, then she puts [tex]y=3\cdot 7=21[/tex] shovels of sand.

Answer: 21 shovels of sand.