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1 Sharon has 25 stickers. She gives
10 stickers to her friend. How many Problem-Solving questions 1 and 2 include:
stickers does she have now?
• Finding 10 more and 10 less than a given two-digit number mentally
15 stickers • Solving word problems concerning finding 10 more and 10 less than a
2 Farrah draws an arrow on a given two-digit number
number line to show 10 more 10 more
than 23. Here is her answer. After children solve the independent practice, make sure they understand how
Is her answer correct? Explain. 23 30 40
No. 10 more than 23 is 33 to count on tens mentally in real-life situations by solving problem 1. Encourage
them to read the situation carefully and guide them to use mental strategies
such as 100 chart or a number line to find 10 less than 25. The answer is 15
stickers.

Vocabulary Check Match. Then have children explore a situation that includes making an inference and
justifying the answer in their own words in problem 2.
count on 10 Encourage children to read and understand the problem carefully and to think
19 29 39 49
about whether Farrah’s words are correct. Encourage them to use the number
line and let them discover that in 10 more, the tens digit increases and in 10
count back 10 less, the tens digit decreases. Farrah’s words are incorrect, as 10 more than 23 is
72 82 92 102
33 not 30.
280
After solving exercises 1 and 2, copy the additional problems below onto the
board for group or individual work. The additional problems are based on
counting on tens. Problems 1 and 2 Ask: How do you find ten more than a
Vocabulary Check number? and How do you find ten less than a number? Encourage them to
use the 100 chart or the number line to find the numbers in each case.
If children struggle to make the matches, If children have difficulty, give them a number line and guide them to count on
review which direction the arrows should go to solve the problems.
when counting on and counting back.
Additional problems 1
Lin has 3 bundles of flowers. She bought one more bundle. How many flowers
does she have in all?
Lin has 3 bundles of flower, which means 30 flowers, and she bought one more
EXIT ACTIVITY bundle, which is 10 more then we can count on one more ten, so that she has
40 flowers in all.

Use the Exit Activity for this lesson to Additional problems 2
reinforce children’s understanding. This A chocolate bar costs 50¢. The chocolate bar company decreased the price
can be used as an informal formative by 10¢. What is the new price of the chocolate bar?
assessment. The price is 50¢. The price decreased by 10¢, so we can count back ten to find
the new price, which is 40¢.

CLOSURE

Make sure children do not have any misconceptions about the main concept of the lesson by asking them to complete the
following: 39, 49___ , ___ , ___

Children should use counting on strategy to find the missing numbers.
Drawing a number line that counts on tens, will help solve the problem as shown.

19 29 39 49 59 69 79 89 99 109

415
415