P 10。 1*2,,2*3,3*4, 4*5......99* 100= 1- 1/2+( 1/2- 1/3)+( 1/3- 1/4)+( 1/4- 1/5)……+( 1/99+ 1 / 100)= 1- 1/ 100=99/ 100

P 17。 Let the original orange be x tons, then (1-40%)x+2.4=80%x solves the equation x= 12, so the original orange has 12 tons.

P2 1。 27 * 6 =162, 23 * 9 = 207207-162 = 459-6 = 3. The new grass is 45÷3= 15 every day.

The original grass is162-15 * 6 = 7221,and the time to eat it is 72 ÷ (21-15) =12 (days).

P27。 1 group: the denominator of the third number 1/3 is 3=2* 1+ 1.

Group II: The denominator of the third number 1/5 is 5=2*2+ 1.

Group III: The denominator of the third number 1/7 is 7=2*3+ 1.

Group 100: denominator of the third number = 2 *100+1= 201.

So the first two denominators are 199,200 respectively, so the sum of the three fractional denominators in the100th array = 199+200+20 1=600.

P28.47/100 = 0.47 0.47/6 * 94 = 0.03, so teachers account for 3% of the total number.

P38。 1. There is no standard answer to this question ... Just be appropriate, such as hard work and success.

Break up completely

I said ... is this a primary school student's homework ... @@@@@@@@@@@@