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1. a) The four consecutive numbers that add up to 130 are 31, 32, 33 and 34.
b) The four consecutive numbers that add up to -38 are -8, -9, -10, -11.

2. 5+6+7+8. 5+6+7=18. 18 is 10 more than 8, the fourth number.

3. (a+d)-(c+b)=0. Being consecutive numbers, a+d will always equal, the same as c+b, meaning subtracting one from the other will be subtracting a number from itself.

4. a+b+c-d=2a. a+b+c-d is equal to a times 2.