- 47 and 37
Solution:
Let l and m respectively be the lower and upper limits of the class. Then the mid-value of the class is $\frac{\text{l+m}}{2}$ and the class-size is (l - m).
Given that the mid-value of the class is 42 and the class-size is 10. Therefore, we have two equations
$\frac{\text{l+m}}{2}=42$
⇒ l + m = 84,
m - l = 10
Adding the above two equations, we have
(l + m) + (m - l) = 84 + 10
⇒ l + m + m - l = 94
⇒ 2m = 94
⇒ l = 37
Substituting the value of m in the first equation, we have
l + 47 = 84
⇒ l = 84 - 47
⇒ l = 37
Hence, the upper and lower limits of the class are 47 and 37 respectively. Thus, the correct choice is (a).