A baby weighs 14 pounds at 5 months and 21 pounds at 10 months. Write an equation that relates the baby's weight, y, to the baby's age, x. Use your equation to find how much the baby weighed at birth.

Question

For the very first thing it asks me to do would I write Y-5=7/5(x-14) Or Y-14=5/7(x-5)?

For the second thing it asks me how would I solve that?

Answer 1

y = mx + b

b, the y intercept, is the weight at birth.

m, the slope is the growth rate

x is the number of months

y is the total weight

14 = 5x + b

21 = 10x + b

2(14 = 5x + b)

28 = 10x + 2b

Now we can subtract one equation from the other:

21 = 10x + b

-(28 = 10x + 2b)

-7 = -b

b = 7, the baby's weight at birth

14 = 5x + 7

5x = 7

x = 7/5, the rate of growth per month