The blog postings are about the Singapore Math. The readers can learn from the postings about Solving Singapore Primary School Mathematics. The blog presenting the Math Concept, Math Questions with solutions that teaches in Singapore Primary Schools. You or the kids can learn the skills of dealing with Math Modeling,Math problem sSolving and Problem Sum from Lower Primary School to Upper Primary School level after reading the blog postings. This posting is an upper primary school math question on Speed.

You can read the posting on **Sarin’s family and Ramadan** and **Sarin’s family celebrating Hari Raya Puasa** in Welcome page about story of Sarin’s family during Ramadan and celebrating Hari Raya Puasa.

Also to read the posting on **Sarin learns rate of change in school (Math Concept) **to learn about concept of speed.

*Challenge yourself to solve the question before look out for the given solution‼*

**Upper primary school mathematics question UPQ275**

Sarin, Hairu and Fatimah were cleaning up their study room during Ramadan. If Sarin, Hairu and Fatimah would take 3 hours, 4 hours and 5hours respectively to clean up the study room if they worked alone. They were to clean the study room with combined effort this time. At 9.30 am, Sarin and Hairu started to clean the room together. At 11 am, Sarin went for a break. Fatimah then took over and worked together with Hairu to complete the rest of the cleaning work. How much time did Hairu and Fatimah take to complete cleaning the rest of the room?

Solution:

The cleaning speed of Sarin = 1/3 room per h

The cleaning speed of Hairu = 1/4 room per h

The cleaning speed of Fatimah = 1/5 room per h

From 9.30 am to 11 am = 1.5 h = 3/2 h

The clean speed of Sarin combined with Hairu = 1/3 + 1/4 = 7/12 room per h

Sarin and Hairu had completed cleaning up 7/12 × 3/2 = 7/8 of the room

Fraction of Room left to clean = 1 – 7/8 = 1/8

The cleaning speed of Hairu combined with Fatimah = 1/4 + 1/5 = 9/20 room per h

Time require to clean 1/8 of the room by Hairu and Fatimah = 1/8 ÷ 9/20 = 1/8 × 20/9 = 5/18 h

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