1) To double the recipe, we are asking to double the amount of sugar (thus making two batches). To do this, we simply multiply #3/4# by #2#:
#3/4times2->3/4times2/1=6/4=3/2#cups or #1 1/2#cups
#---------------------#
2) We can set up the following equation:
#3/4c=4 1/2#
Where:
#>3/4# is the amount of sugar needed to make one batch of cookies
#>c# is the amount of #cups#
#>4 1/2# is how many batches we want to bake
Here, we are simply solving for #c#,
#3/4c=9/2# (Notice how I changed #4 1/2# into an improper fraction)
Cross Multiply:
#"Top Left" times "Bottom Right"="Top Right" times "Bottom Left"#:
#2*3c=9*4#
#6c=36#
Divide #6# to both sides:
#cancel6/cancel6=c=36/6#
#c=6#
Thus we need #6# cups of sugar if we are to make #4 1/2# batches of cookies.
