Addition, Subtraction, Counting Flashcards
Sequencing
I need to identify what date the Friday is given I will start learning a vocabulary set on Monday, January 20th and the duration is five days, including January 20th.
Which number do we include?
The first impulse is to add 5 because I want to study it for 5 days. However, 20+5=25 is Saturday.
When you add 5 to 20 (as in addition), you don’t include the 20th. You give five additional days to the group of 20.
20 21 22 23 24 25
Mo Tu Wd Th Fr Sa
Since we include the 20th ( a 1 additional day), we must subtract 1 from the indermediate result 25 to get 24.
Subtraction
Greg has 16 shells. Joseph has 9 shells fewer than Greg. How many shells does Joseph have?
**1 2 3 4 5 6 78 9 **10 11 12 13 14 15 16
16-9=7
We take away 9 shells (including 9) from the total of 16. We have 7 shells left.
Counting
Roy is standing right in front of Sue. Paul is behind Sue and there are 2 students between them. Paul is the 12th student from the front of the line. How many students are in front of Roy?
- Identify Sue’s position. 12-3=9. We take away 3 persons from the 12 (inclusive), that is Paul and two other students to get the 9th position.
- Roy’s position is 8th.
- There are 7 students in front of Roy because we don’t count him. So, 8-1.
Addition
Marcos saves $8 in March and $11 in April.
How much does he save altogether?
11+8=19. When you add 8 to 11, you don’t count the 11. You give 8 additional dollars to 11 in total.
Sequencing
At a taxi stand, Jenny, who was in the 2nd position, switched places with a disabled man who was in the 9th position. After the man got into a taxi, how many taxis would have to leave until Jenny could get into one?
- After the man gets into the taxi, Jenny’s position becomes 7th. 9-2=7. When we subtract 2 from 9, we take aways 2 taxis (count down from 9 inclusive).
- 7-1=6.
Sequencing
I started taking vitamins B on January 13th. I need to identify for how many days will I be taking them until January 31 inclusive.
31 - 13 = 17 is left inclusive 31 but exclusive of 17. To count 13th of Janury, we add 1. In total, I will be taking vitamins B for 18 days.
Subtract 19 from 34 mentally.
add 1 to 19, add 1 to the intermediate outcome
