What is the distance of 3.6 hours along the river?
(8.2+ 1.3)×3.6
=9.5×3.6
=34.2 km
How many kilometers is it to drive 4.2 hours against the current?
(8.2- 1.3)×4.2
=6.9×4.2
=28.98 km
2.； The distance between the two ants is 175 cm. Big ants crawl 4 cm per second, and small ants crawl 3 cm per second. How many minutes does it take for two ants to meet? How many meters did two ants climb when they met?
Meeting time 175÷(4+3)=25 seconds.
The big ant walked 4×25= 100 meters.
The little ant walked 3×25=75 meters.
3. Xiaoming bought 20 greeting cards at 25. 1 yuan, with small cards at 80 cents each and large cards at 1.5 yuan. How many cards did he buy?
Large greeting card (25.1-0.8× 20) ÷ (1.5-0.8)
=9. 1÷0.7
= 13 sheets
Small greeting card 20- 13=7.
The bottle is full of water, the weight of the bottle is 1.2kg, and the water in the bottle is half. Even the bottle weighs 0.75 kg. How much does this bottle weigh? I calculated 0.15kg. Is that so? )
1.2-( 1.2-0.75)÷( 1- 1/2)
= 1.2-0.45÷0.5
= 1.2-0.9
=0.3 kg