Estimate : 23 × 67
20 (lower down, lower than 5...the last digit) × 70 (Higher, higher than 5)
=20×70
=1400
The estimated value will be 1400
12 boys and 27 girls
1) Add 4 to 9. 13
2) 39 divided by 13 is 3
3)Multiple 3 to 4 boys and 9 girls. 3x4 is 12 boys, 3x9 is 27 girls
Hope this helps!

For each subset it can either contain or not contain an element. For each element, there are 2 possibilities. Multiplying these together we get 27 or 128 subsets. For generalisation the total number of subsets of a set containing n elements is 2 to the power n.
-15 is 15 below o
you are adding 4 , so you are getting closer to 0
so you would actually use subtraction, 15-4 = 11
since 15 is negative, and you are adding a number smaller than 15, the answer would be negative so it would be -11
Exact Form:
13/12
Decimal Form:
1.083
Mixed Number Form:
1 1/12