# Math Help - urgent ~~ Zzz

1. ## urgent ~~ Zzz

i udn understand question.. help mi wif tis questions

2. Hello, xiaoz!

Seven men can paint a bridge in 15 days.
(1) How long woud it take 3 men?

One man can paint $\frac{1}{7}$ of the bridge in 15 days.
In one day, one man can paint $\frac{1}{105}$ of the bridge.

Hence, 3 men can paint $3 \times \frac{1}{105} = \frac{1}{35}$ of the bridge in one day.

Therefore, it will take the 3 men $35$ days to paint the bridge.

(2) The bridge was painted in $t$ days.
Write an expression, in terms of $t$,
for the number of men needed to paint the bridge.

Some information is missing . . .

3. Greetings Xiaoz:

If y varies directly with the square of x, then the relation between x and y is: y = kx^2, where k is a constant. Given y = 10 for some value of x, which I shall call xt, it follows that 10 = k(xt)^2. Now, dividing xt by 2 gives k(xt / 2)^2 on the right. And elimination of parentheses leaves k*(xt)^2 / 4. Hence dividing xt by 2 has the effect of dividing k(xt)^2 by 4. (This is only logical, yes? Dividing a squared quantity by 2 is equivalent to inserting factor, 1/2, within the 'squared parentheses'. The action yields 1/4 upon squaring). Anyway, if k(xt)^2 = 10, then it follows that [k(xt)^2] / 4 = 10/4 = 5/2 or 2.5.

I hope this was instructive.

Rich B.

4. (1b1)
There is an easier method to use rather than Soroban's.

Work is inversely proportional to rate.
Thus, if it takes 15 days for 7 men how long for 3 men and x days.
Since we have a inverse proprtion we know,
$15\times 7=3\times x$
Thus,
$x=35$