Question

20 identical discs are kept over one another. If each disc has a thickness of 0.5 cm, which of the following broken scales can be used to measure the stack of 20 discs in one go?

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Given:
Thichkness of each disc = 0.5 cm
Total number of discs = 20
Total length of stack = 20 x 0.5 = 10 cm

Now, the correct option should have the scale which can measure 10 cm.

• Scale A has full mark from 8 cm to 15 cm. The maximum length this scale can measure = 15 - 8 = 7 cm. So, it is an incorrect option.
• Scale B has full mark from 9 cm to 17 cm. The maximum length this scale can measure = 17 - 9 = 8 cm. So, it is an incorrect option.
• Scale C has full mark from 3 cm to 14 cm. The maximum length this scale can measure = 14 - 3 = 11 cm. This value is more than the required length to be measured. Thus, this is the correct option.
• Scale D has full mark from 3 cm to 10 cm. The maximum length this scale can measure = 10 - 3 = 7 cm. So, it is an incorrect option.