How many tapes needed – Tricky Math Questions

(This is a variation of Singapore PSLE 2017 Math Exam)

Question :

You want 200 ribbons of length 110 cm for a party.
However, the ribbons were sold at 25 m per tape.
How many tapes will you need to buy?

[ Scroll down for the answer  ]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Answer :

You will need to buy 10 Tapes, not 9 !

Some of the Singapore Primary School Students taking the 2017 PSLE (Primary School Leaving Examination)
would have simply perform the following 3 steps :

• Multiply 200 by 110cm and get 22,000cm
• Divide the result 22,000cm by 2,500cm (2.5m x 100cm) and obtain 8.8
• Round up 8.8 to get the answer 9

Unfortunately, 9 is not the correct answer.

How is the answer 10 obtained ?

The 1st step is to determine how many 110cm ribbons can be cut from each 25m tape, hence

• Divide 2,500cm (2.5m x 100cm) by 110cm equals 22.73

Since we require 110cm ribbons, shorter length ribbons are of no use, thus we need to round down
22.73 to get 22 ribbons per 25 m tape.

We need 200 ribbons, thus the next step would be

• Divide 200 ribbons by 22 ribbons equals 9.09 tapes

This time we need to round up 9.09 to obtain 10 tapes as the tapes are only sold in whole at 25 m per tape.

Hence, the answer is 10 tapes!

 

Guess this type of Tricky Math Question is meant to test Students on both Maths and Logical Analytical thinking,

similar to the following questions which trains us to think more deeply and out of the box.