Ben Looi's answer to Keson's Primary 6 Maths Speed question.

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Ben Looi
Ben Looi's answer
18 answers (Tutor Details)
1st
Take their combined sewing rate for 3 hrs.
So in 3 hrs, R can sew 32*3 and 7J can sew 32 buttons. Together they can sew 128 buttons in 3 hrs.
Solve for their combined average speed for sewing 1 button in minutes.
180mins/128= 1.406mins
Multiply by 32 buttons = 45 mins