Mental Math Within 100 — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. A store had 48 apples and sold 19. Which is the best mental step?
A) 48 - 20 + 1
B) 48 + 20 - 1
C) 48 - 20 - 1
D) 48 + 19
48 - 20 is 28, then add 1 back to undo the extra, giving 29 apples left.
2. Leo has 34 stickers. He gets 30 more. How many stickers does he have now?
A) 54
B) 64
C) 66
D) 74
Three jumps of ten from 34 gives 44, 54, 64, so Leo has 64 stickers.
3. What is 25 + 26 using a near-double?
A) 50
B) 51
C) 52
D) 46
Double 25 is 50, and 26 is one more than 25, so the sum is 51.
4. A bus has 72 seats. 28 people get off. Which step is best?
A) 72 - 30 + 2
B) 72 - 30 - 2
C) 72 + 30 - 2
D) 72 - 20 - 8 only
72 - 30 is 42, and adding 2 back gives 44 because 28 is 2 less than 30.
Part B: Fill in the Blank
Write the correct answer on each line.
1. A book has 45 pages. Mia reads 20. Pages left: 45 - 20 = 25.
45, 35, 25 shows two tens removed, so 25 pages are left.
2. Ben had 29 marbles and found 30 more. Using a near-double, the total is 59.
Double 30 is 60, and 29 is one less than 30, so the sum is 59.
3. A bag has 38 candies. You add 19 more. Using compensation, the total is 57.
38 + 20 is 58, and taking back the extra 1 gives 57 candies.
4. A pond has 60 ducks. 25 fly away. Remaining: 35.
60 - 20 is 40, and 40 - 5 is 35, so 35 ducks remain.
5. Tia scored 27 and 27 points on two quizzes. Using doubles her total is 54.
Double 20 is 40 and double 7 is 14, and 40 + 14 is 54, so her total is 54.