Have students draw a house with three numbers inside the roof. Have them write two subtraction problems from the numbers and mentally check each answer by adding the difference and subtrahend. Ask them to write the two addition problems they made to check the problems under the subtraction problems. For example, given 8, 7 and 15 inside the roof leads to the two subtraction problems that students write in the inside of the house: 15-8=7 and 15-7=8. Students check their problems by adding the minuend and subtrahend: 7+8=15 and 8+7=15. They conclude the assignment by writing the two addition problems under the subtraction problems to complete the fact family.
Students work problems in pairs to subtract ones, tens and hundreds with regrouping. They check each digit using addition after regrouping the digits in the minuend in each place. For example, in the subtraction problem where 331 is the minuend and 79 is the subtrahend, students regroup each digit so they can be subtracted. In regrouping, subtraction is done one column at at time. Because the largest number needs to be on top, you might need to borrow from the next column to the left. The result of this regrouping for 331-79 is as follows:
The right column has 11 units of 1s (the original 1 plus 10 from converting one of the 10s in the second column to 10 single units).
The second column has 12 units of tens (2 units of 10 plus 10 more units converted from borrowing one of the 100s from the left column).
The far left column has 2 units of 100 left.
Subtract the 9 from 11 in the single column and get 2. Subtract 7 from 12 in the second column and get 5. Carry over the 2 from the hundreds column. Using this method of regrouping gives you a difference of 242. Check by adding 252 + 79 = 331.
Have a student chart the high and low temperature each day for a month. At month's end, have students find the range of temperature for each day by subtracting the low temperature from the high temperature of that day. Students will check their work by adding the difference to the low temperature for each day of the month. This should result in the high temperature being the answer. Finally, have students find the day with the widest range of temperature.
For example, on the first day of the month the student finds and records the high and low temperature from his city, for example, 81 and 62 on Nov. 1. He repeats that process each day of the month. After the month is over the teacher makes copies of the chart and passes them out to students. Students complete the subtraction problems beginning with the first day of the month, which would be 81-62=19. The student then checks each the answer. For this day it would be 62+19=81. Finally, the student finds the largest difference from the figures calculated on the chart.
Use the data found and calculated for each day of the month from Section 3 to write a word problem about temperature addition -- the process of adding the low temperature and the difference between the high and low temperature -- for 10 of the days of the month. For example, a word problem for one day could be: If the difference between the high and low temperatures on Sept. 8 was 14 degrees and the low temperature was 42 degrees, what was the high temperature?