Page 110 - ICSE Math 8

16. Tap A can fill a cistern in 10 hours while B can empty it in 15 hours. Both the taps are opened simultaneously.
How long would they take to fill the tank?
17. Two pipes A and B can fill a tank in 24 minutes and 32 minutes respectively. If both the pipes are opened
simultaneously, after how much time should B be closed so that the tank is full in 18 minutes?

THINK SMART

1. 8 men and 12 women can do a piece of work in 9 days. 10 men and 20 women can do the same work in
6 days. How long will 5 men and 15 women take to do it?
2. To do a certain work, B would take three times as long as A and C together and C twice as long as A and
B together. The three men together complete the work in 10 days. How long would each take separately
to complete the work?

Maths Lab Activity

Objective: To deduce a direct variation
Material required: Art sheet, coloured sheets of paper, glue stick or fevicol, geometry box
Procedure:

Step 1: Cut six circles of different radii from coloured sheets and paste them on the art sheet.
Step 2: By sliding the ruler on the circles, mark and measure the longest chord, i.e., the diameter of the
circle.
2
Step 3: Using the formula, Area of circle = pr , record areas of all the circles in the given table:
Can you deduce a direct variation between the radius (r) and area of circle (A)?
r
Step 4: Check if is a constant. Radius (r)
A
Step 5: Write all the steps on the art sheet. (in cm)
Area of circle (A)
Result: What can you conclude from this? (in cm )
2

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