Question 252641
Simply add the two fractions {{{3/8}}} and {{{3/5}}} to get: {{{3/8+3/5=(3/8)(5/5)+(3/5)(8/8)=(3*5)/(8*5)+(3*8)/(5*8)=15/40+24/40=(15+24)/40=39/40}}}



So she'll need {{{39/40}}} cups of sugar. Now the question is: which fraction is larger, {{{15/16}}} or {{{39/40}}}?


To answer this question, first assume that they are equal:


{{{15/16=39/40}}}



{{{15*40=39*16}}} Cross multiply



{{{600=624}}} Multiply



{{{600<624}}} Now change the equal sign '=' to a less than sign '<' (since 600 is less than 624).



Because the left side is less than the right, this means that the left side of {{{15/16=39/40}}} is smaller than the right. So change the '=' to a '<' to get {{{15/16<39/40}}}



Since {{{15/16}}} is smaller than {{{39/40}}}, this means that she has less sugar than what she needs. So she does NOT have enough sugar.



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How much does she need then? Well let's figure that out.



To find that out, just subtract the amount she has ({{{15/16}}}) from the amount she needs ({{{39/40}}}) to get: 



{{{39/40-15/16=(39/40)(2/2)-(15/16)(5/5)=(39*2)/(40*2)-(15*5)/(16*5)=78/80-75/80=(78-75)/80=3/80}}}



So she needs {{{3/80}}} of a cup of sugar.