Question

Solve the following questions.
a. A pile of 100 biscuits is 580 mm high. One biscuit is ____ mm thick.
b. A pile of 10 erasers is 9.8 cm high. One eraser is ____ mm thick.
c. A pile of 10 mobile phones is 8 cm high. One phone is ____ mm thick.

Answer 1

Hint: We can solve this question using the unitary method as we have to find the value of a single unit using the value of multiple units. Here the thickness of the multiple units is given in centimetres and the thickness of one unit is asked in millimeters. So we have to convert centimetres into millimeters.

Complete step by step solution:
We are given the thickness of multiple biscuits, erasers, mobile phones. We have to find the thickness of a single biscuit, eraser and mobile phone.
a. Thickness of 100 biscuits is 580 mm.
We have to find the thickness of one biscuit, say x.
$
  100 \to 580\;mm \\
  1 \to x \\
   \Rightarrow x = \dfrac{{580}}{{100}} \\
  \therefore x = 5.8\;mm \;
 $
One biscuit is $5.8\; mm$ thick.
b. Thickness of 10 erasers is 9.8 cm.
We have to find the thickness of one eraser, say y.
One centimetre is equal to 10 millimetres.
9.8 cm is equal to $9.8 \times 10 = 98$ millimetres.
$
  10 \to 98\;mm \\
  1 \to y \\
   \Rightarrow y = \dfrac{{98}}{{10}} \\
  \therefore y = 9.8 \;mm \;
 $
One eraser is 9.8 mm thick.
c. Thickness of 10 mobile phones is 8 cm.
We have to find the thickness of one mobile phone, say z.
One centimetre is equal to 10 millimetres.
8 cm is equal to $8 \times 10 = 80$ millimetres.
$
  10 \to 80mm \\
  1 \to z \\
   \Rightarrow z = \dfrac{{80}}{{10}} \;
  \therefore z = 8\;mm \;
 $
One mobile phone is $8\; mm$ thick.

Note: When using a unitary method, the units of the multiple objects must be the same as the units of the single object and vice-versa else we might get a wrong answer. Here the thickness of the single objects is asked in millimetres, so the known thickness of multiple objects must also be in millimetres. That is why we have converted centimetres into millimetres.