There are 30 flowers. Some have 3 petals and some have 4 petals.All the flowers together have 102 petals. How many flowers have 4 petals?
Let x be the number of flowers with 3 petals and 30-x the number of flowers with 4 petals. We form an equation:
x=18 3 petal flowers,
So there are 30-18=12 4 petal flowers.
You never know when you will need system of equation!
The the number of 3-petal flowers be x, and the number of 4-petal flowers be y.
from here, we know that:
x + y = 30
3x + 4y = 102
Using substitution, we see that:
x = 30 - y
3(30 - y) + 4y = 102
90 - 3y + 4y = 102
90 + y = 102
y = 12
Here are some 4 pétaled flowers for you: