7 + 7+1=15
7+6
Doubles are the facts in which both addends are the same. For example 3+3=6. The doubles plus one are the facts in which one addend is larger than the other by one. Examples 3+4=7, 6+7=13, 5+6=11, 3+2=5. Learning your doubles plus one should involve knowing the doubles and mentally adding the additional one.
4+4
A turn-around fact
7+8=15? Answer is 7+7=14
It is one of several correct interpretations.
7+6
Doubles are the facts in which both addends are the same. For example 3+3=6. The doubles plus one are the facts in which one addend is larger than the other by one. Examples 3+4=7, 6+7=13, 5+6=11, 3+2=5. Learning your doubles plus one should involve knowing the doubles and mentally adding the additional one.
4+4
8-7
A turn-around fact
7+8=15? Answer is 7+7=14
Double 8. Get 16. Subtract 1. Get 15. 8 + 7 = 15
This is the identity property of addition.
7x4=28
Knowing that 6 plus 6 equals 12 helps in solving the near double 6 plus 7 by recognizing that 7 is just one more than 6. Since 6 plus 6 equals 12, you can add one more to that sum to find that 6 plus 7 equals 13. This shows how understanding doubles can simplify calculations involving nearby numbers.
21