Let x be the amount of cement and y be the amount of sand. If <span>the ratio of cement to sand for mortar is 1:3, then 
and y=3x.
</span>
So, if <span>Sandy puts in x=7 shovels of cement, then she puts
shovels of sand.
</span><span>
</span><span>Answer: 21 shovels of sand.
</span>
</span>
So, if <span>Sandy puts in x=7 shovels of cement, then she puts
</span><span>
</span><span>Answer: 21 shovels of sand.
</span>
