Before each calculation, look for a key step that can help you work the entire calculation in your head. Perform the calculation, and show the key step that makes it easier.

		answer	key step
ex.	6 + 2 + 1 =	10	6 + 1 = 8  or   + = 1
1.	3.8 + 5 + 6.2 =	_________	_______________
2.	(2.8 + 5) + =	_________	_______________
3.	7 . 5 + 7 . 4 =	_________	_______________
4.	3( + ) =	_________	_______________
5.	4 + 10 + 3 =	_________	_______________
6.	8 . 6 + 1 . 6 =	_________	_______________
7.	6.9 + (3 + 2) =	_________	_______________
8.	177 . 31 + 69 . 177 =	_________	_______________
9.	57(100 + 1) =	_________	_______________
10.	3( + 1) =	_________	_______________
11.	.5 × 6 × 10 =	_________	_______________
12.	( × 3) × =	_________	_______________
13.	22(4 + ) =	_________	_______________
14.	44 × 2 =	_________	_______________
15.	35(10 - ) =	_________	_______________

	key step
1.	Rearrange the terms.
2.	Parentheses don’t matter here. (Why?)
3.	Factoring gives 7 . (    +    .
4.	3 ×    + 3 ×
5.	Rearrange terms.
6.	Find a common factor.
7.	Look at the first two terms.
8.	Factor.
9.	Don’t add first.
10.	Don’t add first.
11.	Rearrange.
12.	Ignore parentheses. (Why is that ok?)
13.	Don’t add first.
14.	Think of 44 × 2 as 44 . (2 + ).
15.	Don’t subtract first.

		answer	key step
1.	3.8 + 5 + 6.2 =	15	.2 + .8  or  3.8 + 6.2
2.	(2.8 + 5) + =	8.8	+
3.	7 . 5 + 7 . 4 =	70	5 + 4
4.	3( + ) =	1	multiply through to get 1 +
5.	4 + 10 + 3 =	18	+
6.	8 . 6 + 1 . 6 =	65	8 + 1
7.	6.9 + (3 + 2) =	12	6.9 + 3.1
8.	177 . 31 + 69 . 177 =	17700	31 + 69
9.	57(100 + 1) =	5757	57 . 100 + 57 . 1
10.	3( + 1) =	4	.   +   3 . 1   =    1 + 3
11.	.5 × 6 × 10 =	30	.5 × 10
12.	( × 3) × =		×
13.	22(4 + ) =	99	22 ×
14.	44 × 2 =	99	44 ×
15.	35(10 - ) =	345	350 - . 35

		answer	key step
1.	3.8 + 5 + 6.2 =	15	.2 + .8 = 1 or 3.8 + 6.2 = 10
2.	(2.8 + 5) + =	8.8	5 + = 6
3.	7 . 5 + 7 . 4 =	70	7 . (5 + 4) = 7 . 10
4.	3( + ) =	1	3 . + 3 . = 1 +
5.	4 + 10 + 3 =	18	4 + 3 = 7 = 8
6.	8 . 6 + 1 . 6 =	65	(8 + 1) . 6 = 10 . 6.5
7.	6.9 + (3 + 2) =	12	6.9 + 3 = 6.9 + 3.1 = 10
8.	177 . 31 + 69 . 177 =	17700	177 . (31 + 69) = 177 . 100
9.	57(100 + 1) =	5757	57 . 100 + 57 . 1
10.	3( + 1) =	4	3 = and . = 1
	so 3( + 1) =	.   +	3 . 1   =    1 + 3
11.	.5 × 6 × 10 =	30	.5 × 6 × 10 = (.5 × 10) × 6
12.	( × 3) × =		3 × = × = 1
13.	22(4 + ) =	99	22 × = 11
14.	44 × 2 =	99	44 × = 11
15.	35(10 - ) =	345	350 - . 35