Answer is 1:4
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Step-by-step explanation:
1/5 of the beans are mung, so 4/5 of the beans are pinto. The two fractions add to 5/5 = 1.
Ignore the denominators and focus on the numerators for each fraction. We have 1 mung and 4 pinto. The values are read in this order to form the ratio 1:4 which is our answer. We cannot reduce this ratio any further.
The order is important because saying 4:1 would mean that we have 4 mung beans and 1 pinto, when it's the other way around.
Side note: The value 450 isn't needed. We could easily change it to any other multiple of 5 and get the same exact answer.