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After birth, a baby's weight increased at a steady rate for several weeks.

A linear model of this situation contains the values (1, 7.2) and (7, 9), where x represents the number of weeks, and y represents the baby's weight, in pounds.

What was the baby's weight at birth?
0.3 of a pound
6 pounds
7.2 pounds
6.9 pounds

Question

MEDAL AND FAN REWARDED FOR CORRECT ANSWERRRRRRRRRRRRRRRRRR CX
After birth, a baby's weight increased at a steady rate for several weeks. 

A linear model of this situation contains the values (1, 7.2) and (7, 9), where x represents the number of weeks, and y represents the baby's weight, in pounds.

What was the baby's weight at birth?
0.3 of a pound
6 pounds
7.2 pounds
6.9 pounds

anonymous · Answer

@KamiBug @Catlover5925

kamibug · Answer

That's when x equals 0, so basically it's asking for the y-intercept. To find the y-intercept you need to know the slope.
9 - 7.2 / 7 - 1 = 0.3
Then use the slope formula and other known info to find the value of the y-intercept. 
You can use either of the points but I'll use (7, 9).
9 - x / 7 - 0 = 0.3 
^ Solve this equation for x and you'll get your answer. :)

catlover5925 · Answer

ok so 7.2 is at one week so you know it has to be less than that, I think it would be 6.9 because I took 9 - 7.2 and got1.8 then divided that by 7 weeks and got 0.25 then I took 7.2 and subtracted it by 0.25