Answer: 20
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Step-by-step explanation:
a,b,c,d are consecutive whole numbers. This means one follows right after the other. Example: 5,6,7,8 or 50,51,52,53
In general we have:
- a = some whole number
- b = a+1
- c = b+1 = (a+1)+1 = a+2
- d = c+1 = (a+2)+1 = a+3
The sequence a,b,c,d is the same as a,a+1,a+2,a+3
Add those expressions together and set the sum equal to 78. Then solve for 'a'.
a+b+c+d = 78
a+(a+1)+(a+2)+(a+3) = 78
4a+6 = 78
4a = 78-6
4a = 72
a = 72/4
a = 18
This leads to
- b = a+1 = 18+1 = 19
- c = a+2 = 18+2 = 20 which is the answer
- d = a+3 = 18+3 = 21
The four consecutive whole numbers for a,b,c,d are 18,19,20,21 in that order.
As a check,
a+b+c+d = 18+19+20+21 = 78
which confirms our answer.