Solution:
Number of TVs produced in the seventh year = 1000
Number of TVs produced in the tenth year = 1450
t7 = 1000
t10 = 1450
a + 6 d = 1000 ----- (1)
a + 9 d = 1450 ----- (2)
(1) – (2)
Subtracting second equation from first equation
a + 6 d = 1000
a + 9 d = 1450
(-) (-) (-)
------------------
-3d = -450
d = -450/(-3)
d = 150
Substitute d = 150 in the first equation
a + 6(150) = 1000
a + 900 = 1000
a = 1000 -900
a = 100
Therefore number of TVs produced on the first year is 100
To find number of TVs produced in the 15th year year we have to find the 15th term of the A.P
tn = a + (n-1) d
t15 = 100 + (15-1) 150
t15 = 100 + 14(150)
= 100 + 2100
= 2200