Question

Carpenter $A$ can make a chair in $6$ hours, carpenter $B$ in $7$ hours and carpenter $C$ in $8$ hours. If each carpenter works for $8$ hours per day, how many chairs will be made in $21$ day?

• A. $61$
• B. $67$
• C. $73$
• D. $79$

Answer 1

The correct option is C $73$

In $6$ hours, the number of chairs made by carpenter $A$ is one.

Therefore, in $(21\times 8)$ hours, number of chairs made by $A$ is:

$\frac{21\times 8}{6}=\frac{168}{6}=28$

Similarly, number of chairs made by $B$ is:

$\frac{21\times 8}{7}=\frac{168}{7}=24$

And, number of chairs made by $C$ is:

$\frac{21\times 8}{8}=\frac{168}{8}=21$

thus, the total number of chairs made in $21$ days are $28+24+21=73$

Hence, $73$ chairs made in $21$ days.