Please attempt the above question, timed and then click below to reveal the few second technique leading to the correct answer ==>
Technique © :
Step 1. Total mass of all fifteen children =>
3 1/3 x15 = 50 stones
Step 2. Total mass of ten girls in school year 4 = 50 stones (the answer from step 1) – total mass of five boys in school year 5 (5 x 4 =20 stones) =>
50 – 20 = 30 stones
Step 3. Therefore, the average mass of ten girls in school year 4 is equal to =>
30 / 10 =3 stones
Answer: => Three (3) stones.
Time allowed: 30 seconds
Time taken using the technique: 3 seconds
Time saved = 27 seconds [9/10th (90%) of time allowed by examiner]
Note: If you want, you can prove your answer in the following way:
Total mass of boys = 5 x 4 =20 stones
Total mass of girls = 10 x 3 = 30 stones
The total mass of 15 children is 50 (20 + 30) stones
Therefore, the average mass of 15 children is 50 / 15 = 3 1/3 stones. Thus, we have proved it back to the fact given in the question.
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WORK SHEET – Practice question
Six boys in school year 5 and ten girls in school year 4 have an average mass of three and a half stones. The average mass of ten girls in school year 4 is 3.2 stones. Find the average mass of six boys in school year 5?
Technique © :
Step 1. =>
Step 2. =>
Step 3. =>
Answer: =>
