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Lusine saw birds and mice eating seeds on the ground. She calculated 12 heads and 39 legs in total. How many birds and mice are on the ground?

Sagot :

Answer:

4.5 birds, 7.5 mice

Step-by-step explanation:

We know that birds have 2 legs and mice have 4. Furthermore, birds have 1 head as well as mice.

If b represents the amount of birds and m represents the amount of mice, because there are only birds and mice here, the total amount of birds and mice (b + m) must equal 12.

b + m = 12

Next, to find the total amount of bird legs, we must add 2 legs for each bird. Another way of putting this is to multiply 2 by the amount of birds, or b * 2. Similarly, the amount of mice legs is equal to m * 4. The total amount of legs is equal to 39, so

2b + 4m = 39

Our two equations are thus

b + m = 12

2b + 4m = 39

One way to solve this is to solve for m in the first equation and plug that into the second. We have

b + m = 12

subtract b from both sides

m = 12-b

substitute that into the second equation

2b + 4(12-b) = 39

2b + 48 - 4b = 39

-2b + 48 = 39

subtract 48 from both sides to isolate the b and its coefficient

-2b = -9

divide both sides by -2 to isolate b

b = 4.5

Therefore, there are 4.5 birds on the ground (there is somehow a half of a bird!)

Plugging that into m = 12-b, we have m = 12-4.5 = 7.5