Understand the rule first
A ratio tells you the relative number of equal parts. Add the parts for a total share, find the value of one part, then scale each group.
Use equal parts to share quantities and scale relationships accurately.
A ratio tells you the relative number of equal parts. Add the parts for a total share, find the value of one part, then scale each group.
Using the ratio numbers as the actual amounts instead of as numbers of equal parts.
Reusable method: Label what one part represents before scaling.There are seven equal parts altogether.
Answer C: £45
2 + 5 = 7; £63 ÷ 7 = £9 per part; 5 × £9 = £45.
Quick method: Label what one part represents before scaling.
Four parts represent 24 beads.
Answer A: 18
One part is 24 ÷ 4 = 6; red beads = 3 × 6 = 18.
Quick method: Label what one part represents before scaling.
Multiply each map centimetre by six kilometres.
Answer C: 45 km
7.5 × 6 = 45 km.
Quick method: Label what one part represents before scaling.
Nine parts represent all 54 people.
Answer D: 42
2 + 7 = 9; 54 ÷ 9 = 6; children = 7 × 6 = 42.
Quick method: Label what one part represents before scaling.
Three parts represent 15 ml; then find all eight parts.
Answer D: 40 ml
One part is 15 ÷ 3 = 5 ml. Eight parts make 8 × 5 = 40 ml.
Quick method: Label what one part represents before scaling.
There are seven equal parts altogether.
Answer A: 36
84 ÷ 7 = 12 per part; the smaller share is 3 × 12 = 36.
Quick method: Label what one part represents before scaling.
Find the mass represented by one part.
Answer B: 300 g
Five parts equal 750 g, so one part is 150 g. Sugar is two parts: 300 g.
Quick method: Label what one part represents before scaling.
Find the value of one of the 16 equal parts.
Answer C: 8
64 ÷ 16 = 4 per part. The difference is two parts, so 2 × 4 = 8.
Quick method: Label what one part represents before scaling.
Convert 7.6 × 50,000 cm into kilometres.
Answer D: 3.8 km
7.6 × 50,000 = 380,000 cm = 3,800 m = 3.8 km.
Quick method: Label what one part represents before scaling.
The blue amount is unchanged, so keep its seven parts fixed.
Answer A: 66
The added red counters increase red from four parts to five parts, so one part is 6. Originally there were 11 parts: 11 × 6 = 66.
Quick method: Label what one part represents before scaling.