Adding and Subtracting Fractions with Unlike Denominators — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Tina used 23 cup sugar for cookies and 34 cup for cake from 2 cups total. How much is left?
A) 712 cup
B) 512 cup
C) 12 cup
D) 1 cup
LCD of 3 and 4 is 12. 23+34=812+912=1712=1512. Used from 2 cups: 2−1512=2412−1712=712 cup left.
2. A recipe needs 58 cup milk. James poured 13 cup. How much more does he need?
A) 724 cup
B) 45 cup
C) 14 cup
D) 28 cup
LCD of 8 and 3 is 24. 58=1524, 13=824. Needed: 1524−824=724 cup.
3. Sam walked 310 + 25 mi. Kai walked 45 mi. Who walked farther and by how much?
A) Kai by 110 mi
B) Sam by 110 mi
C) Kai by 310 mi
D) They walked the same
Sam: 310+25=310+410=710. Kai: 45=810. Kai walked more by 810−710=110 mile.
4. A board is 78 yd. A carpenter cuts 13 yd then 16 yd. How much remains in simplest form?
A) 38 yard
B) 524 yard
C) 14 yard
D) 724 yard
Total cut: 13+16=26+16=36=12. Remaining: 78−12=78−48=38 yard.
Part B: Fill in the Blank
Write the correct answer on each line.
1. Rosa ate 14 of a pizza and her brother ate 13. Together they ate 712 of the pizza.
LCD of 4 and 3 is 12. 14=312, 13=412. Together: 312+412=712.
2. A tank is 56 full. After using 14 of the tank, it is 712 full.
LCD of 6 and 4 is 12. 56=1012, 14=312. Remaining: 1012−312=712.
3. Lee hiked 35 of a trail in the morning and 14 more after lunch. He hiked 1720 in all.
LCD of 5 and 4 is 20. 35=1220, 14=520. Total: 1220+520=1720.
4. A ribbon is 78 yard long. After cutting off 25 yard, 1940 yard remains.
LCD of 8 and 5 is 40. 78=3540, 25=1640. Remaining: 3540−1640=1940.
5. Two friends used 23 lb and 512 lb of flour. They used 1112 pounds total.
LCD of 3 and 12 is 12. 23=812. Total: 812+512=1312=1112 pounds.