Lecture: Combined Operations: Addition and Subtraction
• To solve a problem using both addition and subtraction, solve from left to
right as they come.
Examples:
1. Mark had ₱75. He spent ₱30 to buy a pencil case. His mother gave him ₱50
later that day. How much money did Mark have then?
₱75 – ₱30 + ₱50 = _____
Step 1 – Subtract
₱ 75
- ₱ 30
₱45
2.
Step 2 – Add
₱45
+ ₱50
₱95
Dina had ₱95.
26 – 13 + 11= ____
Step 1 – Subtract
Step 2 – Add
26
– 13
13
13
+ 11
24
3. 318 + 29 – 88 = ____
Step 1 – Add
318 + 29 = 347
Step 2 – Subtract
347 – 88 = 259
4. 14 + 14 – 11 = 17
• In an expression like 36 – ( 14 + 11) , the part of Mathematical expression
within the parenthesis is calculated first ( 14 + 11) = 25, then this result is
used to calculate the rest of the expression 36 – 25 = 11.
Therefore, 36 – ( 14 + 11) = 11
1. Mr. Santos has 286 trees in his orchard. Eighty-nine of these trees are
mangoes and 74 are chicos. How many are atis trees?
286 – ( 89 + 74 ) = _____
Step 1 – Add
89 + 74 = 163
Step 2 – Subtract
286 – 163 = 123
There are 123 atis trees.
2. 185 – ( 25 + 17 ) = 185 – 42 = 143
3. 45 + ( 23 – 20 ) = 45 + 3 = 48