Compatible
Numbers
Mental Math Monday!
Sunday, November 15, 15
Compatible Numbers
✦
✦
Compatible numbers are sometimes referred to
as friendly numbers or nice numbers.
This strategy involves looking for pairs of
numbers that will combine to make a friendly
sum.
Example:
Sunday, November 15, 15
3+8+7+6+2
Example:
✦
3+8+7+6+2
Which numbers combine to make friendly
sums?
✦
8 + 2 = 10
✦
7 + 3 = 10
✦
Now all that’s left is 6!
10 + 10 + 6 = 26!
Sunday, November 15, 15
Compatible Numbers
Example #2:
25 + 47 + 75
*HINT: Look for numbers that will add to give
you a sum that ends with a zero!
?
Sunday, November 15, 15
Compatible Numbers
Example #2:
25 + 47 + 75
25 + 75 = 100
100 + 47 = 147!!
Sunday, November 15, 15
Your Turn!
a) 1 + 2 + 9 =
b)11 + 2 + 59 =
c) 75 + 95 + 25 =
d) 80 + 20 + 79 =
e) 125 + 25 + 33 =
f) 60 + 30 + 40 =
g) 4400 + 1600 + 3000 =
h) 3250 + 3000 + 1750 =
Sunday, November 15, 15
a) 1 + 2 + 9 = 9 + 1 = 10,
b)11 + 2 + 59 = 11+59 = 70,
10 + 2 = 12
70 + 2 = 72
c) 75 + 95 + 25 = 75 + 25 = 100, 100 +95 = 195
d) 80 + 20 + 79 = 80 + 20= 100, 100 + 79 = 179
e) 125 + 25 + 33 = 125+25 =150, 150 + 33 = 183
f) 60 + 30 + 40 = 60+40= 100, 100 + 30 = 130
g) 4400 + 1600 + 3000 = 4400+1600=6000, 6000+3000
= 9000
h) 3250 + 3000 + 1750 = 3250+1750=5000, 5000+3000
=8000
Sunday, November 15, 15
Your Turn!
a) 0.6 + 0.9 + 0.4 =
b)0.2 + 0.4 + 0.8 + 0.6=
c) 0.7 + 0.1 + 0.9 + 0.3 =
d) 0.2 + 0.4 + 0.3 + 0.8 + 0.6 =
e) 0.25 + 0.5 + 0.75 =
f) 0.45 + 0.63 + 0.05 =
Sunday, November 15, 15
a) 0.6 + 0.9 + 0.4 = 0.6+0.4 = 1.0, 1.0+0.9 =1.9
b)0.2 + 0.4 + 0.8 + 0.6= 0.2+0.8=1.0, 0.4+0.6 = 1.0,
1.0+1.0=2.0
c) 0.7 + 0.1 + 0.9 + 0.3= 0.7+0.3=1.0, 0.1+0.9=1.0,
1.0+1.0=2.0
d) 0.2 + 0.4 + 0.3 + 0.8 + 0.6 = 0.2+0.8=1.0, 0.4+0.6 =
1.0, 1.0+1.0+0.3 = 2.3
e) 0.25 + 0.5 + 0.75 = 0.25+0.75=1.0, 1.0+0.5 = 1.5
f) 0.45 + 0.63 + 0.05 = 0.45+0.05=1.50, 1.50+0.63 =2.13
Sunday, November 15, 15