Five boys in school year 5 and ten girls in school year 4 have an average mass of three and one third stones. The average mass of five boys in school year 5 is four stones. Find the average mass of ten girls in school year 4?

Please attempt the above question, timed and then click below to reveal the few second technique leading to the correct answer ==>

Hours:Minutes:Seconds
00:00:00 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

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. =>