Mrs.D Math · 7th Grade

CROSS
LAB

Proportions & Ratios
a
b
=
c
d
→
a × d = b × c
Cross Multiply!
✖ Solve Proportion
÷ Simplify Ratio
⚖ Is it a Proportion?
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📚 Proportions & Ratios

✖ Solving a Proportion

1
Cross multiply: multiply the diagonal pairs.
3/4 = x/20   →   3 × 20 = 4 × x
2
Solve for x: divide both sides by the coefficient of x.
60 = 4x   →   x = 15

÷ Simplifying a Ratio

1
Find the GCF of both numbers.
12 : 18   →   GCF = 6
2
Divide both parts by the GCF.
12 ÷ 6 : 18 ÷ 6   →   2 : 3

⚖ Is it a Proportion?

1
Cross multiply both pairs.
2/5 and 4/10   →   2×10 = 20   5×4 = 20
2
If the products are equal it is a proportion. If not, it is not.
20 = 20 ✓   →   Yes, they are proportional!
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