Answer:
300 : 900
Explanation:
sum the parts of the ratio , 1 + 3 = 4 parts
Divide the amount by 4 to find the value of one part of the ratio
1200 ÷ 4 = 300 ← value of 1 part of the ratio , then
3 parts = 3 × 300 = 900
1200 in the ratio 1 : 3 is 300 : 900