r is a number of raspberries.
b is a number of blackberries.
¨There are 7 more raspberries than blackberries ¨ means r-b =7.
¨there are 13 berries in all¨ means r+b = 13.
So we have 2 equation.
r-b=7
r+b=13.
If we need to know values of r and b, we need to solve this system of equations.
r-b=7
r+b=13
2r =20
r=10,
r-b = 7, 10-b =7, b=3.
r=10 and b=3
Let's denote r as raspberries and b as blackberries. We know that there are 7 more raspberries than blackberries, so we can write:
r = 7 + b
Or:
r - b = 7
There are 13 berries in all, which means:
r + b = 13
Now, this is just a system of linear equations:
r - b = 7
r + b = 13
Subtract the two equations:
-2b = -6
Divide by -2:
b = 3
There are 3 blackberries.
